[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v7 34/42] Postcopy: Use helpers to map pages dur
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v7 34/42] Postcopy: Use helpers to map pages during migration |
Date: |
Thu, 6 Aug 2015 12:22:01 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* Amit Shah (address@hidden) wrote:
> On (Tue) 16 Jun 2015 [11:26:47], Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > In postcopy, the destination guest is running at the same time
> > as it's receiving pages; as we receive new pages we must put
> > them into the guests address space atomically to avoid a running
> > CPU accessing a partially written page.
> >
> > Use the helpers in postcopy-ram.c to map these pages.
> >
> > qemu_get_buffer_less_copy is used to avoid a copy out of qemu_file
> > in the case that postcopy is going to do a copy anyway.
> >
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>
>
> > @@ -1881,6 +1890,16 @@ static int ram_load(QEMUFile *f, void *opaque, int
> > version_id)
> > int flags = 0, ret = 0;
> > static uint64_t seq_iter;
> > int len = 0;
> > + /*
> > + * System is running in postcopy mode, page inserts to host memory
> > must be
> > + * atomic
> > + */
>
> *If* system is running in postcopy mode ....
Done.
> > + MigrationIncomingState *mis = migration_incoming_get_current();
> > + bool postcopy_running = postcopy_state_get(mis) >=
> > + POSTCOPY_INCOMING_LISTENING;
> > + void *postcopy_host_page = NULL;
> > + bool postcopy_place_needed = false;
> > + bool matching_page_sizes = qemu_host_page_size == TARGET_PAGE_SIZE;
> >
> > seq_iter++;
> >
> > @@ -1896,13 +1915,57 @@ static int ram_load(QEMUFile *f, void *opaque, int
> > version_id)
> > rcu_read_lock();
> > while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) {
> > ram_addr_t addr, total_ram_bytes;
> > - void *host;
> > + void *host = 0;
> > + void *page_buffer = 0;
> > + void *postcopy_place_source = 0;
> > uint8_t ch;
> > + bool all_zero = false;
> >
> > addr = qemu_get_be64(f);
> > flags = addr & ~TARGET_PAGE_MASK;
> > addr &= TARGET_PAGE_MASK;
> >
> > + if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE |
> > + RAM_SAVE_FLAG_XBZRLE)) {
> > + host = host_from_stream_offset(f, mis, addr, flags);
> > + if (!host) {
> > + error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
> > + ret = -EINVAL;
> > + break;
> > + }
>
> So the host_from_stream_offset was moved here from below. One
> invocation below is still left, which is a bug..
Thanks, fixed.
> > + if (!postcopy_running) {
> > + page_buffer = host;
> > + } else {
>
> Instead of this, can we just do:
>
> page_buffer = host;
> if (postcopy_running) {
done.
> > + /*
> > + * Postcopy requires that we place whole host pages
> > atomically.
> > + * To make it atomic, the data is read into a temporary
> > page
> > + * that's moved into place later.
> > + * The migration protocol uses, possibly smaller,
> > target-pages
> > + * however the source ensures it always sends all the
> > components
> > + * of a host page in order.
> > + */
> > + if (!postcopy_host_page) {
> > + postcopy_host_page = postcopy_get_tmp_page(mis);
> > + }
> > + page_buffer = postcopy_host_page +
> > + ((uintptr_t)host & ~qemu_host_page_mask);
> > + /* If all TP are zero then we can optimise the place */
> > + if (!((uintptr_t)host & ~qemu_host_page_mask)) {
> > + all_zero = true;
> > + }
> > +
> > + /*
> > + * If it's the last part of a host page then we place the
> > host
> > + * page
> > + */
> > + postcopy_place_needed = (((uintptr_t)host +
> > TARGET_PAGE_SIZE) &
> > + ~qemu_host_page_mask) == 0;
> > + postcopy_place_source = postcopy_host_page;
> > + }
> > + } else {
> > + postcopy_place_needed = false;
> > + }
>
> ... and similar for postcopy_place_needed as well? It becomes much
> easier to read.
Done; actually it's just not needed at all - the function entry initialisation
of that flag is sufficient.
> > case RAM_SAVE_FLAG_COMPRESS_PAGE:
> > - host = host_from_stream_offset(f, addr, flags);
> > + all_zero = false;
> > + if (postcopy_running) {
> > + error_report("Compressed RAM in postcopy mode @%zx\n",
> > addr);
> > + return -EINVAL;
> > + }
> > + host = host_from_stream_offset(f, mis, addr, flags);
>
> This line should go (as mentioned above)?
Yes, done.
Dave
>
>
> Amit
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
[Prev in Thread] |
Current Thread |
[Next in Thread] |
- Re: [Qemu-devel] [PATCH v7 34/42] Postcopy: Use helpers to map pages during migration,
Dr. David Alan Gilbert <=