RE: [PATCH v6 6/7] migration/multifd: implement qpl compression and decompression

[Liu, Yuan1]

> -----Original Message-----
> From: Fabiano Rosas <farosas@suse.de>
> Sent: Tuesday, May 14, 2024 10:08 PM
> To: Liu, Yuan1 <yuan1.liu@intel.com>; peterx@redhat.com
> Cc: qemu-devel@nongnu.org; Zou, Nanhai <nanhai.zou@intel.com>
> Subject: RE: [PATCH v6 6/7] migration/multifd: implement qpl compression
> and decompression
> 
> "Liu, Yuan1" <yuan1.liu@intel.com> writes:
> 
> >> -----Original Message-----
> >> From: Fabiano Rosas <farosas@suse.de>
> >> Sent: Monday, May 13, 2024 11:14 PM
> >> To: Liu, Yuan1 <yuan1.liu@intel.com>; peterx@redhat.com
> >> Cc: qemu-devel@nongnu.org; Liu, Yuan1 <yuan1.liu@intel.com>; Zou,
> Nanhai
> >> <nanhai.zou@intel.com>
> >> Subject: Re: [PATCH v6 6/7] migration/multifd: implement qpl
> compression
> >> and decompression
> >>
> >> Yuan Liu <yuan1.liu@intel.com> writes:
> >>
> >> > each qpl job is used to (de)compress a normal page and it can
> >> > be processed independently by the IAA hardware. All qpl jobs
> >> > are submitted to the hardware at once, and wait for all jobs
> >> > completion. If hardware path(IAA) is not available, use software
> >> > for compression and decompression.
> >> >
> >> > Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
> >> > Reviewed-by: Nanhai Zou <nanhai.zou@intel.com>
> >> > ---
> >> >  migration/multifd-qpl.c | 284
> +++++++++++++++++++++++++++++++++++++++-
> >> >  1 file changed, 280 insertions(+), 4 deletions(-)
> >> >
> >> > diff --git a/migration/multifd-qpl.c b/migration/multifd-qpl.c
> >> > index 89fa51091a..9a1fddbdd0 100644
> >> > --- a/migration/multifd-qpl.c
> >> > +++ b/migration/multifd-qpl.c
> >> > @@ -13,6 +13,7 @@
> >> >  #include "qemu/osdep.h"
> >> >  #include "qemu/module.h"
> >> >  #include "qapi/error.h"
> >> > +#include "exec/ramblock.h"
> >> >  #include "migration.h"
> >> >  #include "multifd.h"
> >> >  #include "qpl/qpl.h"
> >> > @@ -204,6 +205,139 @@ static void
> >> multifd_qpl_send_cleanup(MultiFDSendParams *p, Error **errp)
> >> >      p->iov = NULL;
> >> >  }
> >> >
> >> > +/**
> >> > + * multifd_qpl_prepare_job: prepare a compression or decompression
> job
> >> > + *
> >> > + * Prepare a compression or decompression job and configure job
> >> attributes
> >> > + * including job compression level and flags.
> >> > + *
> >> > + * @job: pointer to the QplData structure
> >>
> >> qpl_job structure
> >
> > Thanks for the comment, I will fix this next version.
> >
> >> > + * @is_compression: compression or decompression indication
> >> > + * @input: pointer to the input data buffer
> >> > + * @input_len: the length of the input data
> >> > + * @output: pointer to the output data buffer
> >> > + * @output_len: the size of the output data buffer
> >> > + */
> >> > +static void multifd_qpl_prepare_job(qpl_job *job, bool
> is_compression,
> >> > +                                    uint8_t *input, uint32_t
> input_len,
> >> > +                                    uint8_t *output, uint32_t
> >> output_len)
> >> > +{
> >> > +    job->op = is_compression ? qpl_op_compress : qpl_op_decompress;
> >> > +    job->next_in_ptr = input;
> >> > +    job->next_out_ptr = output;
> >> > +    job->available_in = input_len;
> >> > +    job->available_out = output_len;
> >> > +    job->flags = QPL_FLAG_FIRST | QPL_FLAG_LAST |
> QPL_FLAG_OMIT_VERIFY;
> >> > +    /* only supports one compression level */
> >> > +    job->level = 1;
> >> > +}
> >> > +
> >> > +/**
> >> > + * multifd_qpl_build_packet: build a qpl compressed data packet
> >> > + *
> >> > + * The qpl compressed data packet consists of two parts, one part
> >> stores
> >> > + * the compressed length of each page, and the other part is the
> >> compressed
> >> > + * data of each page. The zbuf_hdr stores the compressed length of
> all
> >> pages,
> >> > + * and use a separate IOV to store the compressed data of each page.
> >> > + *
> >> > + * @qpl: pointer to the QplData structure
> >> > + * @p: Params for the channel that we are using
> >> > + * @idx: The index of the compressed length array
> >> > + * @addr: pointer to the compressed data
> >> > + * @len: The length of the compressed data
> >> > + */
> >> > +static void multifd_qpl_build_packet(QplData *qpl, MultiFDSendParams
> >> *p,
> >> > +                                     uint32_t idx, uint8_t *addr,
> >> uint32_t len)
> >> > +{
> >> > +    qpl->zbuf_hdr[idx] = cpu_to_be32(len);
> >> > +    p->iov[p->iovs_num].iov_base = addr;
> >> > +    p->iov[p->iovs_num].iov_len = len;
> >> > +    p->iovs_num++;
> >> > +    p->next_packet_size += len;
> >> > +}
> >> > +
> >> > +/**
> >> > + * multifd_qpl_compress_pages: compress normal pages
> >> > + *
> >> > + * Each normal page will be compressed independently, and the
> >> compression jobs
> >> > + * will be submitted to the IAA hardware in non-blocking mode,
> waiting
> >> for all
> >> > + * jobs to be completed and filling the compressed length and data
> into
> >> the
> >> > + * sending IOVs. If IAA device is not available, the software path
> is
> >> used.
> >> > + *
> >> > + * Returns 0 for success or -1 for error
> >> > + *
> >> > + * @p: Params for the channel that we are using
> >> > + * @errp: pointer to an error
> >> > + */
> >> > +static int multifd_qpl_compress_pages(MultiFDSendParams *p, Error
> >> **errp)
> >> > +{
> >> > +    qpl_status status;
> >> > +    QplData *qpl = p->compress_data;
> >> > +    MultiFDPages_t *pages = p->pages;
> >> > +    uint8_t *zbuf = qpl->zbuf;
> >> > +    uint8_t *host = pages->block->host;
> >> > +    uint32_t job_num = pages->normal_num;
> >>
> >> A bit misleading because job_num is used in the previous patch as a
> >> synonym for page_count. We could change the previous patch to:
> >> multifd_qpl_init(uint32_t page_count, ...
> >
> > Yes, I will replace job_num with page_count for multifd_qpl_init next
> version.
> >
> >> > +    qpl_job *job = NULL;
> >> > +
> >> > +    assert(job_num <= qpl->total_job_num);
> >> > +    /* submit all compression jobs */
> >> > +    for (int i = 0; i < job_num; i++) {
> >> > +        job = qpl->job_array[i];
> >> > +        multifd_qpl_prepare_job(job, true, host + pages->offset[i],
> >> > +                                p->page_size, zbuf, p->page_size -
> 1);
> >>
> >> Isn't the output buffer size == page size, why the -1?
> >
> > I think the compressed data should be smaller than a normal page.
> > If the compressed data size is equal to a normal page, send the original
> > page directly to avoid decompression operation.
> >
> > If the output buffer size is set to p->page_size, the compressed data
> size
> > may be greater than or equal to a normal page, then there are two
> conditions for
> > sending a normal page, one is job status == QPL_STS_OK and job-
> >total_out == p->page_size,
> > another is job status == QPL_STS_MORE_OUTPUT_NEEDED.
> >
> > If the output buffer size is p->page_size - 1, only check
> QPL_STS_MORE_OUTPUT_NEEDED is ok.
> > I will add comments for this in the next version.
> >
> 
> Thanks.
> 
> >> > +        /* if hardware path(IAA) is unavailable, call the software
> path
> >> */
> >>
> >> If we're doing the fallback automatically, isn't that what
> qpl_path_auto
> >> does already? What's the difference between the two approaches?
> >
> > The qpl_path_auto feature currently has some limitations.
> >
> > Limitation 1: it does not detect IAA device status before job
> submission, which means
> > I need to use qpl_init_job(qpl_path_hardware, ...) first to make sure
> the hardware path
> > is available, then qpl_path_auto can work for software fallback when
> submitting a job to
> > the IAA fails.
> >
> > Limitation 2: The job submission API has changed
> > For the qpl_path_hardware, the qpl_submit_job is a non-blocking
> function, only submitting
> > a job to IAA work queues, use qpl_wait_job to get the job result.
> >
> > For qpl_path_software/auto, the qpl_submit_job is a blocking function
> and returns the job
> > result directly,  qpl_wait_job can't get the job result.
> >
> > In short, the qpl_submit_job/qpl_wait_job APIs do not well support the
> qpl_path_auto feature.
> 
> Please put a summary of this in the commit message so in the future we
> can evaluate whether to continue checking for ourselves.

Sure, I will add a summary in the commit message.
I confirmed with the QPL development team that, sw fallback for
qpl_submit_job/qpl_wait_job APIs will be ready next QPL release. So I will
keep the current design next version, the software path only for the QPL unit 
test.

After the next version of QPL is released, I will update the sw fallback code
so that sw fallback can be used both in the QPL unit test and migration with 
IAA.

> >> > +        if (!qpl->iaa_avail) {
> >>
> >> This function got a bit convoluted, it's probably worth a check at the
> >> start and a branch to different multifd_qpl_compress_pages_slow()
> >> routine altogether.
> >
> > I agree that using multifd_qpl_compress_pages_slow is a better choice.
> >
> > In my previous thoughts, the QPl software path(or slow path) is only
> used
> > for the unit test and I did not consider fallback to the software path
> when
> > migration start because the QPL software path has no advantage over
> zstd.
> > So when the work queue is full, always try to resubmit the job instead
> of
> > fallback software path.
> >
> > I now realize that when IAA hardware throughput is the bottleneck(the
> work queue is full),
> > switching to software may also increase performance.
> >
> > I will implement the automatically falling back to the software when IAA
> work
> > queue is full into the next version and update the performance data.
> With the
> > increase in mutlfd migration threads, the performance will be better
> than now.
> > Currently, 4 threads will reach the IAA device throughput bottleneck,
> then increasing
> > The number of threads does not increase any performance.
> >
> >> > +            status = qpl_execute_job(job);
> >> > +            if (status == QPL_STS_OK) {
> >> > +                multifd_qpl_build_packet(qpl, p, i, zbuf, job-
> >> >total_out);
> >> > +            } else if (status == QPL_STS_MORE_OUTPUT_NEEDED) {
> >> > +                /* compressed length exceeds page size, send page
> >> directly */
> >> > +                multifd_qpl_build_packet(qpl, p, i, host + pages-
> >> >offset[i],
> >> > +                                         p->page_size);
> >> > +            } else {
> >> > +                error_setg(errp, "multifd %u: qpl_execute_job
> >> error %d",
> >> > +                           p->id, status);
> >> > +                return -1;
> >> > +            }
> >> > +            zbuf += p->page_size;
> >> > +            continue;
> >> > +        }
> >> > +retry:
> >> > +        status = qpl_submit_job(job);
> >> > +        if (status == QPL_STS_OK) {
> >> > +            zbuf += p->page_size;
> >> > +        } else if (status == QPL_STS_QUEUES_ARE_BUSY_ERR) {
> >> > +            goto retry;
> >>
> >> A retry count here would be nice.
> >
> > As the previous comment, I will switch to
> multifd_qpl_compress_pages_slow
> > When the work queue is full, I will give a performance comparison
> between
> > hardware only and software fallback next version.
> >
> >> > +        } else {
> >> > +            error_setg(errp, "multifd %u: qpl_submit_job failed with
> >> error %d",
> >> > +                       p->id, status);
> >> > +            return -1;
> >> > +        }
> >> > +    }
> >> > +    if (!qpl->iaa_avail) {
> >> > +        goto done;
> >> > +    }
> >> > +    /* wait all jobs to complete for hardware(IAA) path */
> >> > +    for (int i = 0; i < job_num; i++) {
> >> > +        job = qpl->job_array[i];
> >> > +        status = qpl_wait_job(job);
> >> > +        if (status == QPL_STS_OK) {
> >> > +            multifd_qpl_build_packet(qpl, p, i, qpl->zbuf + (p-
> >> >page_size * i),
> >> > +                                     job->total_out);
> >> > +        } else if (status == QPL_STS_MORE_OUTPUT_NEEDED) {
> >> > +            /* compressed data length exceeds page size, send page
> >> directly */
> >> > +            multifd_qpl_build_packet(qpl, p, i, host + pages-
> >> >offset[i],
> >> > +                                     p->page_size);
> >> > +        } else {
> >> > +            error_setg(errp, "multifd %u: qpl_wait_job failed with
> >> error %d",
> >> > +                       p->id, status);
> >> > +            return -1;
> >> > +        }
> >> > +    }
> >> > +done:
> >> > +    return 0;
> >> > +}
> >> > +
> >> >  /**
> >> >   * multifd_qpl_send_prepare: prepare data to be able to send
> >> >   *
> >> > @@ -217,8 +351,28 @@ static void
> >> multifd_qpl_send_cleanup(MultiFDSendParams *p, Error **errp)
> >> >   */
> >> >  static int multifd_qpl_send_prepare(MultiFDSendParams *p, Error
> **errp)
> >> >  {
> >> > -    /* Implement in next patch */
> >> > -    return -1;
> >> > +    QplData *qpl = p->compress_data;
> >> > +    uint32_t hdr_size;
> >> > +
> >> > +    if (!multifd_send_prepare_common(p)) {
> >> > +        goto out;
> >> > +    }
> >> > +
> >> > +    assert(p->pages->normal_num <= qpl->total_job_num);
> >> > +    hdr_size = p->pages->normal_num * sizeof(uint32_t);
> >> > +    /* prepare the header that stores the lengths of all compressed
> >> data */
> >> > +    p->iov[1].iov_base = (uint8_t *) qpl->zbuf_hdr;
> >> > +    p->iov[1].iov_len = hdr_size;
> >>
> >> Better use p->iovs_num here in case we ever decide to add more stuff to
> >> the front of the array.
> >
> > Get it, I will fix this next version.
> >
> >> > +    p->iovs_num++;
> >> > +    p->next_packet_size += hdr_size;
> >>
> >> Here's the first time we're setting this value, right? So just a
> regular
> >> attribution(=).
> >
> > Yes, I will fix this next version.
> >
> >> > +    if (multifd_qpl_compress_pages(p, errp) != 0) {
> >> > +        return -1;
> >> > +    }
> >> > +
> >> > +out:
> >> > +    p->flags |= MULTIFD_FLAG_QPL;
> >> > +    multifd_send_fill_packet(p);
> >> > +    return 0;
> >> >  }
> >> >
> >> >  /**
> >> > @@ -256,6 +410,88 @@ static void
> >> multifd_qpl_recv_cleanup(MultiFDRecvParams *p)
> >> >      p->compress_data = NULL;
> >> >  }
> >> >
> >> > +/**
> >> > + * multifd_qpl_decompress_pages: decompress normal pages
> >> > + *
> >> > + * Each compressed page will be decompressed independently, and the
> >> > + * decompression jobs will be submitted to the IAA hardware in non-
> >> blocking
> >> > + * mode, waiting for all jobs to be completed and loading the
> >> decompressed
> >> > + * data into guest memory. If IAA device is not available, the
> software
> >> path
> >> > + * is used.
> >> > + *
> >> > + * Returns 0 for success or -1 for error
> >> > + *
> >> > + * @p: Params for the channel that we are using
> >> > + * @errp: pointer to an error
> >> > + */
> >> > +static int multifd_qpl_decompress_pages(MultiFDRecvParams *p, Error
> >> **errp)
> >> > +{
> >> > +    qpl_status status;
> >> > +    qpl_job *job;
> >> > +    QplData *qpl = p->compress_data;
> >> > +    uint32_t job_num = p->normal_num;
> >> > +    uint32_t off = 0;
> >> > +
> >> > +    assert(job_num <= qpl->total_job_num);
> >> > +    /* submit all decompression jobs */
> >> > +    for (int i = 0; i < job_num; i++) {
> >> > +        /* if the data size is the same as the page size, load it
> >> directly */
> >> > +        if (qpl->zbuf_hdr[i] == p->page_size) {
> >> > +            memcpy(p->host + p->normal[i], qpl->zbuf + off, p-
> >> >page_size);
> >> > +            off += p->page_size;
> >> > +            continue;
> >> > +        }
> >> > +        job = qpl->job_array[i];
> >> > +        multifd_qpl_prepare_job(job, false, qpl->zbuf + off, qpl-
> >> >zbuf_hdr[i],
> >> > +                                p->host + p->normal[i], p-
> >page_size);
> >> > +        /* if hardware path(IAA) is unavailable, call the software
> path
> >> */
> >> > +        if (!qpl->iaa_avail) {
> >> > +            status = qpl_execute_job(job);
> >> > +            if (status == QPL_STS_OK) {
> >> > +                off += qpl->zbuf_hdr[i];
> >> > +                continue;
> >> > +            }
> >> > +            error_setg(errp, "multifd %u: qpl_execute_job failed
> with
> >> error %d",
> >> > +                       p->id, status);
> >> > +            return -1;
> >> > +        }
> >> > +retry:
> >> > +        status = qpl_submit_job(job);
> >> > +        if (status == QPL_STS_OK) {
> >> > +            off += qpl->zbuf_hdr[i];
> >> > +        } else if (status == QPL_STS_QUEUES_ARE_BUSY_ERR) {
> >> > +            goto retry;
> >> > +        } else {
> >> > +            error_setg(errp, "multifd %u: qpl_submit_job failed with
> >> error %d",
> >> > +                       p->id, status);
> >> > +            return -1;
> >> > +        }
> >> > +    }
> >> > +    if (!qpl->iaa_avail) {
> >> > +        goto done;
> >> > +    }
> >> > +    /* wait all jobs to complete for hardware(IAA) path */
> >> > +    for (int i = 0; i < job_num; i++) {
> >> > +        if (qpl->zbuf_hdr[i] == p->page_size) {
> >> > +            continue;
> >> > +        }
> >> > +        job = qpl->job_array[i];
> >> > +        status = qpl_wait_job(job);
> >> > +        if (status != QPL_STS_OK) {
> >> > +            error_setg(errp, "multifd %u: qpl_wait_job failed with
> >> error %d",
> >> > +                       p->id, status);
> >> > +            return -1;
> >> > +        }
> >> > +        if (job->total_out != p->page_size) {
> >> > +            error_setg(errp, "multifd %u: decompressed len %u,
> expected
> >> len %u",
> >> > +                       p->id, job->total_out, p->page_size);
> >> > +            return -1;
> >> > +        }
> >> > +    }
> >> > +done:
> >> > +    return 0;
> >> > +}
> >> > +
> >> >  /**
> >> >   * multifd_qpl_recv: read the data from the channel into actual
> pages
> >> >   *
> >> > @@ -269,8 +505,48 @@ static void
> >> multifd_qpl_recv_cleanup(MultiFDRecvParams *p)
> >> >   */
> >> >  static int multifd_qpl_recv(MultiFDRecvParams *p, Error **errp)
> >> >  {
> >> > -    /* Implement in next patch */
> >> > -    return -1;
> >> > +    QplData *qpl = p->compress_data;
> >> > +    uint32_t in_size = p->next_packet_size;
> >> > +    uint32_t flags = p->flags & MULTIFD_FLAG_COMPRESSION_MASK;
> >> > +    uint32_t hdr_len = p->normal_num * sizeof(uint32_t);
> >> > +    uint32_t data_len = 0;
> >> > +    int ret;
> >> > +
> >> > +    if (flags != MULTIFD_FLAG_QPL) {
> >> > +        error_setg(errp, "multifd %u: flags received %x flags
> >> expected %x",
> >> > +                   p->id, flags, MULTIFD_FLAG_QPL);
> >> > +        return -1;
> >> > +    }
> >> > +    multifd_recv_zero_page_process(p);
> >> > +    if (!p->normal_num) {
> >> > +        assert(in_size == 0);
> >> > +        return 0;
> >> > +    }
> >> > +
> >> > +    /* read compressed data lengths */
> >> > +    assert(hdr_len < in_size);
> >> > +    ret = qio_channel_read_all(p->c, (void *) qpl->zbuf_hdr,
> hdr_len,
> >> errp);
> >> > +    if (ret != 0) {
> >> > +        return ret;
> >> > +    }
> >> > +    assert(p->normal_num <= qpl->total_job_num);
> >>
> >> I'm still in doubt whether we should use p->page_count directly all
> >> over. It's nice to move the concept into the QPL domain space, but it
> >> makes less sense in these functions that take MultiFD*Params as
> >> argument.
> >
> > I don't understand what you mean here. Do you plan to remove page_count
> from MultiFD*Params
> > and provide a new API to get the migrated page count?
> >
> 
> No, I mean that qpl->total_job_num == p->page_count, so we could use
> p->page_count in the functions that have MultiFDParams available. Maybe
> even drop total_job_num altogether. But I'm debating if it is worth it,
> because that makes the code more coupled to multifd and we may not want
> that. Let's leave it for now.

Get it, thanks for the comment

> >> > +    for (int i = 0; i < p->normal_num; i++) {
> >> > +        qpl->zbuf_hdr[i] = be32_to_cpu(qpl->zbuf_hdr[i]);
> >> > +        data_len += qpl->zbuf_hdr[i];
> >> > +        assert(qpl->zbuf_hdr[i] <= p->page_size);
> >> > +    }
> >> > +
> >> > +    /* read compressed data */
> >> > +    assert(in_size == hdr_len + data_len);
> >> > +    ret = qio_channel_read_all(p->c, (void *) qpl->zbuf, data_len,
> >> errp);
> >> > +    if (ret != 0) {
> >> > +        return ret;
> >> > +    }
> >> > +
> >> > +    if (multifd_qpl_decompress_pages(p, errp) != 0) {
> >> > +        return -1;
> >> > +    }
> >> > +    return 0;
> >> >  }
> >> >
> >> >  static MultiFDMethods multifd_qpl_ops = {