Re: [External] Re: [PATCH v2 07/20] util/dsa: Implement DSA device start and stop logic.

[Hao Xiang]

On Mon, Dec 11, 2023 at 1:28 PM Fabiano Rosas <farosas@suse.de> wrote:
>
> Hao Xiang <hao.xiang@bytedance.com> writes:
>
> > * DSA device open and close.
> > * DSA group contains multiple DSA devices.
> > * DSA group configure/start/stop/clean.
> >
> > Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
> > Signed-off-by: Bryan Zhang <bryan.zhang@bytedance.com>
> > ---
> >  include/qemu/dsa.h |  49 +++++++
> >  util/dsa.c         | 338 +++++++++++++++++++++++++++++++++++++++++++++
> >  util/meson.build   |   1 +
> >  3 files changed, 388 insertions(+)
> >  create mode 100644 include/qemu/dsa.h
> >  create mode 100644 util/dsa.c
> >
> > diff --git a/include/qemu/dsa.h b/include/qemu/dsa.h
> > new file mode 100644
> > index 0000000000..30246b507e
> > --- /dev/null
> > +++ b/include/qemu/dsa.h
> > @@ -0,0 +1,49 @@
> > +#ifndef QEMU_DSA_H
> > +#define QEMU_DSA_H
> > +
> > +#include "qemu/thread.h"
> > +#include "qemu/queue.h"
> > +
> > +#ifdef CONFIG_DSA_OPT
> > +
> > +#pragma GCC push_options
> > +#pragma GCC target("enqcmd")
> > +
> > +#include <linux/idxd.h>
> > +#include "x86intrin.h"
> > +
> > +#endif
> > +
> > +/**
> > + * @brief Initializes DSA devices.
> > + *
> > + * @param dsa_parameter A list of DSA device path from migration parameter.
>
> This code seems pretty generic, let's decouple this doc from migration.
>
> > + * @return int Zero if successful, otherwise non zero.
> > + */
> > +int dsa_init(const char *dsa_parameter);
> > +
> > +/**
> > + * @brief Start logic to enable using DSA.
> > + */
> > +void dsa_start(void);
> > +
> > +/**
> > + * @brief Stop logic to clean up DSA by halting the device group and 
> > cleaning up
> > + * the completion thread.
>
> "Stop the device group and the completion thread"
>
> The mention of "clean/cleaning up" makes this confusing because of
> dsa_cleanup() below.

Fixed.

>
> > + */
> > +void dsa_stop(void);
> > +
> > +/**
> > + * @brief Clean up system resources created for DSA offloading.
> > + *        This function is called during QEMU process teardown.
>
> This is not called during QEMU process teardown. It's called at the end
> of migration AFAICS. Maybe just leave this sentence out.

Fixed.

>
> > + */
> > +void dsa_cleanup(void);
> > +
> > +/**
> > + * @brief Check if DSA is running.
> > + *
> > + * @return True if DSA is running, otherwise false.
> > + */
> > +bool dsa_is_running(void);
> > +
> > +#endif
> > \ No newline at end of file
> > diff --git a/util/dsa.c b/util/dsa.c
> > new file mode 100644
> > index 0000000000..8edaa892ec
> > --- /dev/null
> > +++ b/util/dsa.c
> > @@ -0,0 +1,338 @@
> > +/*
> > + * Use Intel Data Streaming Accelerator to offload certain background
> > + * operations.
> > + *
> > + * Copyright (c) 2023 Hao Xiang <hao.xiang@bytedance.com>
> > + *                    Bryan Zhang <bryan.zhang@bytedance.com>
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a 
> > copy
> > + * of this software and associated documentation files (the "Software"), 
> > to deal
> > + * in the Software without restriction, including without limitation the 
> > rights
> > + * to use, copy, modify, merge, publish, distribute, sublicense, and/or 
> > sell
> > + * copies of the Software, and to permit persons to whom the Software is
> > + * furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice shall be included 
> > in
> > + * all copies or substantial portions of the Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS 
> > OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> > + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR 
> > OTHER
> > + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
> > FROM,
> > + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS 
> > IN
> > + * THE SOFTWARE.
> > + */
> > +
> > +#include "qemu/osdep.h"
> > +#include "qemu/queue.h"
> > +#include "qemu/memalign.h"
> > +#include "qemu/lockable.h"
> > +#include "qemu/cutils.h"
> > +#include "qemu/dsa.h"
> > +#include "qemu/bswap.h"
> > +#include "qemu/error-report.h"
> > +#include "qemu/rcu.h"
> > +
> > +#ifdef CONFIG_DSA_OPT
> > +
> > +#pragma GCC push_options
> > +#pragma GCC target("enqcmd")
> > +
> > +#include <linux/idxd.h>
> > +#include "x86intrin.h"
> > +
> > +#define DSA_WQ_SIZE 4096
> > +#define MAX_DSA_DEVICES 16
> > +
> > +typedef QSIMPLEQ_HEAD(dsa_task_queue, buffer_zero_batch_task) 
> > dsa_task_queue;
> > +
> > +struct dsa_device {
> > +    void *work_queue;
> > +};
> > +
> > +struct dsa_device_group {
> > +    struct dsa_device *dsa_devices;
> > +    int num_dsa_devices;
> > +    uint32_t index;
> > +    bool running;
> > +    QemuMutex task_queue_lock;
> > +    QemuCond task_queue_cond;
> > +    dsa_task_queue task_queue;
> > +};
> > +
> > +uint64_t max_retry_count;
> > +static struct dsa_device_group dsa_group;
> > +
> > +
> > +/**
> > + * @brief This function opens a DSA device's work queue and
> > + *        maps the DSA device memory into the current process.
> > + *
> > + * @param dsa_wq_path A pointer to the DSA device work queue's file path.
> > + * @return A pointer to the mapped memory.
> > + */
> > +static void *
> > +map_dsa_device(const char *dsa_wq_path)
> > +{
> > +    void *dsa_device;
> > +    int fd;
> > +
> > +    fd = open(dsa_wq_path, O_RDWR);
> > +    if (fd < 0) {
> > +        fprintf(stderr, "open %s failed with errno = %d.\n",
> > +                dsa_wq_path, errno);
>
> Use error_report and error_setg* for these. Throughout the series.

All converted to using error_report.

>
> > +        return MAP_FAILED;
> > +    }
> > +    dsa_device = mmap(NULL, DSA_WQ_SIZE, PROT_WRITE,
> > +                      MAP_SHARED | MAP_POPULATE, fd, 0);
> > +    close(fd);
> > +    if (dsa_device == MAP_FAILED) {
> > +        fprintf(stderr, "mmap failed with errno = %d.\n", errno);
> > +        return MAP_FAILED;
> > +    }
> > +    return dsa_device;
> > +}
> > +
> > +/**
> > + * @brief Initializes a DSA device structure.
> > + *
> > + * @param instance A pointer to the DSA device.
> > + * @param work_queue  A pointer to the DSA work queue.
> > + */
> > +static void
> > +dsa_device_init(struct dsa_device *instance,
> > +                void *dsa_work_queue)
> > +{
> > +    instance->work_queue = dsa_work_queue;
> > +}
> > +
> > +/**
> > + * @brief Cleans up a DSA device structure.
> > + *
> > + * @param instance A pointer to the DSA device to cleanup.
> > + */
> > +static void
> > +dsa_device_cleanup(struct dsa_device *instance)
> > +{
> > +    if (instance->work_queue != MAP_FAILED) {
> > +        munmap(instance->work_queue, DSA_WQ_SIZE);
> > +    }
> > +}
> > +
> > +/**
> > + * @brief Initializes a DSA device group.
> > + *
> > + * @param group A pointer to the DSA device group.
> > + * @param num_dsa_devices The number of DSA devices this group will have.
> > + *
> > + * @return Zero if successful, non-zero otherwise.
> > + */
> > +static int
> > +dsa_device_group_init(struct dsa_device_group *group,
> > +                      const char *dsa_parameter)
>
> The documentation doesn't match the signature. This happens in other
> places as well, please review all of them.
>
Fixed all cases.

> > +{
> > +    if (dsa_parameter == NULL || strlen(dsa_parameter) == 0) {
> > +        return 0;
> > +    }
> > +
> > +    int ret = 0;
> > +    char *local_dsa_parameter = g_strdup(dsa_parameter);
> > +    const char *dsa_path[MAX_DSA_DEVICES];
> > +    int num_dsa_devices = 0;
> > +    char delim[2] = " ";
>
> So we're using space separated strings. Let's document this in this file
> and also on the migration parameter documentation.

Fixed.

>
> > +
> > +    char *current_dsa_path = strtok(local_dsa_parameter, delim);
> > +
> > +    while (current_dsa_path != NULL) {
> > +        dsa_path[num_dsa_devices++] = current_dsa_path;
> > +        if (num_dsa_devices == MAX_DSA_DEVICES) {
> > +            break;
> > +        }
> > +        current_dsa_path = strtok(NULL, delim);
> > +    }
> > +
> > +    group->dsa_devices =
> > +        malloc(sizeof(struct dsa_device) * num_dsa_devices);
>
> Use g_new0() here.

Converted to use g_new0 and g_free accordingly.

>
> > +    group->num_dsa_devices = num_dsa_devices;
> > +    group->index = 0;
> > +
> > +    group->running = false;
> > +    qemu_mutex_init(&group->task_queue_lock);
> > +    qemu_cond_init(&group->task_queue_cond);
> > +    QSIMPLEQ_INIT(&group->task_queue);
> > +
> > +    void *dsa_wq = MAP_FAILED;
> > +    for (int i = 0; i < num_dsa_devices; i++) {
> > +        dsa_wq = map_dsa_device(dsa_path[i]);
> > +        if (dsa_wq == MAP_FAILED) {
> > +            fprintf(stderr, "map_dsa_device failed MAP_FAILED, "
> > +                    "using simulation.\n");
>
> What does "using simulation" means? And how are doing it by returning -1
> from this function?

* "using simulation" was a copy and paste mistake. Removed that.
* -1 is an error code and will be propagated from
dsa_device_group_init to dsa_init and eventually to
multifd_load_setup/multifd_save_setup.
multifd_load_setup/multifd_save_setup now checks the return code from
dsa_init and aborts the migration if dsa_init fails.

>
> > +            ret = -1;
>
> What about the memory for group->dsa_devices in the failure case? We
> should either free it here or make sure the client code calls the
> cleanup routines.

In the failure case, dsa_device_group_cleanup will free the
group->dsa_devices memory allocation. dsa_device_group_cleanup is
called by dsa_cleanup. multifd_load_cleanup/multifd_save_cleanup will
call the cleanup routines.

>
> > +            goto exit;
> > +        }
> > +        dsa_device_init(&dsa_group.dsa_devices[i], dsa_wq);
> > +    }
> > +
> > +exit:
> > +    g_free(local_dsa_parameter);
> > +    return ret;
> > +}
> > +
> > +/**
> > + * @brief Starts a DSA device group.
> > + *
> > + * @param group A pointer to the DSA device group.
> > + * @param dsa_path An array of DSA device path.
> > + * @param num_dsa_devices The number of DSA devices in the device group.
> > + */
> > +static void
> > +dsa_device_group_start(struct dsa_device_group *group)
> > +{
> > +    group->running = true;
> > +}
> > +
> > +/**
> > + * @brief Stops a DSA device group.
> > + *
> > + * @param group A pointer to the DSA device group.
> > + */
> > +__attribute__((unused))
> > +static void
> > +dsa_device_group_stop(struct dsa_device_group *group)
> > +{
> > +    group->running = false;
> > +}
> > +
> > +/**
> > + * @brief Cleans up a DSA device group.
> > + *
> > + * @param group A pointer to the DSA device group.
> > + */
> > +static void
> > +dsa_device_group_cleanup(struct dsa_device_group *group)
> > +{
> > +    if (!group->dsa_devices) {
> > +        return;
> > +    }
> > +    for (int i = 0; i < group->num_dsa_devices; i++) {
> > +        dsa_device_cleanup(&group->dsa_devices[i]);
> > +    }
> > +    free(group->dsa_devices);
> > +    group->dsa_devices = NULL;
> > +
> > +    qemu_mutex_destroy(&group->task_queue_lock);
> > +    qemu_cond_destroy(&group->task_queue_cond);
> > +}
> > +
> > +/**
> > + * @brief Returns the next available DSA device in the group.
> > + *
> > + * @param group A pointer to the DSA device group.
> > + *
> > + * @return struct dsa_device* A pointer to the next available DSA device
> > + *         in the group.
> > + */
> > +__attribute__((unused))
> > +static struct dsa_device *
> > +dsa_device_group_get_next_device(struct dsa_device_group *group)
> > +{
> > +    if (group->num_dsa_devices == 0) {
> > +        return NULL;
> > +    }
> > +    uint32_t current = qatomic_fetch_inc(&group->index);
>
> The name "index" alone feels a bit opaque. Is there a more
> representative name we could give it?

I renamed it to device_allocator_index and added a comment to explain the field.

>
> > +    current %= group->num_dsa_devices;
> > +    return &group->dsa_devices[current];
> > +}
> > +
> > +/**
> > + * @brief Check if DSA is running.
> > + *
> > + * @return True if DSA is running, otherwise false.
> > + */
> > +bool dsa_is_running(void)
> > +{
> > +    return false;
> > +}
> > +
> > +static void
> > +dsa_globals_init(void)
> > +{
> > +    max_retry_count = UINT64_MAX;
> > +}
> > +
> > +/**
> > + * @brief Initializes DSA devices.
> > + *
> > + * @param dsa_parameter A list of DSA device path from migration parameter.
> > + * @return int Zero if successful, otherwise non zero.
> > + */
> > +int dsa_init(const char *dsa_parameter)
> > +{
> > +    dsa_globals_init();
> > +
> > +    return dsa_device_group_init(&dsa_group, dsa_parameter);
> > +}
> > +
> > +/**
> > + * @brief Start logic to enable using DSA.
> > + *
> > + */
> > +void dsa_start(void)
> > +{
> > +    if (dsa_group.num_dsa_devices == 0) {
> > +        return;
> > +    }
> > +    if (dsa_group.running) {
> > +        return;
> > +    }
> > +    dsa_device_group_start(&dsa_group);
> > +}
> > +
> > +/**
> > + * @brief Stop logic to clean up DSA by halting the device group and 
> > cleaning up
> > + * the completion thread.
> > + *
> > + */
> > +void dsa_stop(void)
> > +{
> > +    struct dsa_device_group *group = &dsa_group;
> > +
> > +    if (!group->running) {
> > +        return;
> > +    }
> > +}
> > +
> > +/**
> > + * @brief Clean up system resources created for DSA offloading.
> > + *        This function is called during QEMU process teardown.
> > + *
> > + */
> > +void dsa_cleanup(void)
> > +{
> > +    dsa_stop();
> > +    dsa_device_group_cleanup(&dsa_group);
> > +}
> > +
> > +#else
> > +
> > +bool dsa_is_running(void)
> > +{
> > +    return false;
> > +}
> > +
> > +int dsa_init(const char *dsa_parameter)
> > +{
> > +    fprintf(stderr, "Intel Data Streaming Accelerator is not supported "
> > +                    "on this platform.\n");
> > +    return -1;
>
> Nothing checks this later in the series and we end up trying to start a
> migration when we shouldn't. Fixing the configure step would already
> stop this happening, but make sure you check this anyway and abort the
> migration.

multifd_load_setup/multifd_save_setup now checks the return code from
dsa_init and aborts the migration if dsa_init fails. The
non-CONFIG_DSA_OPT version of dsa_init should really just be a no-op.
Changed that.

>
> > +}
> > +
> > +void dsa_start(void) {}
> > +
> > +void dsa_stop(void) {}
> > +
> > +void dsa_cleanup(void) {}
> > +
> > +#endif
>
> These could all be in the header.

The function definitions are already in dsa.h Do you mean moving the
function implementations to the header as well?

>
> > +
> > diff --git a/util/meson.build b/util/meson.build
> > index c2322ef6e7..f7277c5e9b 100644
> > --- a/util/meson.build
> > +++ b/util/meson.build
> > @@ -85,6 +85,7 @@ if have_block or have_ga
> >  endif
> >  if have_block
> >    util_ss.add(files('aio-wait.c'))
> > +  util_ss.add(files('dsa.c'))
>
> I find it clearer to add the file conditionally under CONFIG_DSA_OPT
> here and remove the ifdef from the C file. I'm not sure if we have any
> guidelines for this, so up to you.
>
> >    util_ss.add(files('buffer.c'))
> >    util_ss.add(files('bufferiszero.c'))
> >    util_ss.add(files('hbitmap.c'))