> Subject: Re: [QEMU 1/7] balloon: speed up inflating & deflating process
>
> On 13.06.2016 12:16, Liang Li wrote:
> > The implementation of the current virtio-balloon is not very
> > efficient, Bellow is test result of time spends on inflating the
> > balloon to 3GB of a 4GB idle guest:
> >
> > a. allocating pages (6.5%, 103ms)
> > b. sending PFNs to host (68.3%, 787ms) c. address translation (6.1%,
> > 96ms) d. madvise (19%, 300ms)
> >
> > It takes about 1577ms for the whole inflating process to complete. The
> > test shows that the bottle neck is the stage b and stage d.
> >
> > If using a bitmap to send the page info instead of the PFNs, we can
> > reduce the overhead spends on stage b quite a lot. Furthermore, it's
> > possible to do the address translation and do the madvise with a bulk
> > of pages, instead of the current page per page way, so the overhead of
> > stage c and stage d can also be reduced a lot.
> >
> > This patch is the QEMU side implementation which is intended to speed
> > up the inflating & deflating process by adding a new feature to the
> > virtio-balloon device. And now, inflating the balloon to 3GB of a 4GB
> > idle guest only takes 210ms, it's about 8 times as fast as before.
> >
> > TODO: optimize stage a by allocating/freeing a chunk of pages instead
> > of a single page at a time.
> >
> > Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> > ---
> > hw/virtio/virtio-balloon.c | 159 ++++++++++++++++++++----
> > include/standard-headers/linux/virtio_balloon.h | 1 +
> > 2 files changed, 139 insertions(+), 21 deletions(-)
> >
> > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> > index 8c15e09..8cf74c2 100644
> > --- a/hw/virtio/virtio-balloon.c
> > +++ b/hw/virtio/virtio-balloon.c
> > @@ -47,6 +47,76 @@ static void balloon_page(void *addr, int deflate)
> > #endif }
> >
> > +static void do_balloon_bulk_pages(ram_addr_t base_pfn, int page_shift,
> > + unsigned long len, bool deflate) {
> > + ram_addr_t size, processed, chunk, base;
> > + void *addr;
> > + MemoryRegionSection section = {.mr = NULL};
> > +
> > + size = (len << page_shift);
> > + base = (base_pfn << page_shift);
> > +
> > + for (processed = 0; processed < size; processed += chunk) {
> > + chunk = size - processed;
> > + while (chunk >= TARGET_PAGE_SIZE) {
> > + section = memory_region_find(get_system_memory(),
> > + base + processed, chunk);
> > + if (!section.mr) {
> > + chunk = QEMU_ALIGN_DOWN(chunk / 2, TARGET_PAGE_SIZE);
> > + } else {
> > + break;
> > + }
> > + }
> > +
> > + if (section.mr &&
> > + (int128_nz(section.size) && memory_region_is_ram(section.mr))) {
> > + addr = section.offset_within_region +
> > + memory_region_get_ram_ptr(section.mr);
> > + qemu_madvise(addr, chunk,
> > + deflate ? QEMU_MADV_WILLNEED :
> QEMU_MADV_DONTNEED);
> > + } else {
> > + fprintf(stderr, "can't find the chunk, skip\n");
>
> Please try to avoid new fprintf(stderr, ...) in the QEMU sources.
> Use error_report(...) or in this case maybe rather
> qemu_log_mask(LOG_GUEST_ERROR, ...) instead, and try to use a more
> reasonable error message (e.g. that it is clear that the error happened in the
> balloon code).
>
Indeed, the error message is no good, will change in next version.
> > + chunk = TARGET_PAGE_SIZE;
> > + }
> > + }
> > +}
> > +
> > +static void balloon_bulk_pages(ram_addr_t base_pfn, unsigned long
> *bitmap,
> > + unsigned long len, int page_shift,
> > +bool deflate) { #if defined(__linux__)
>
> Why do you need this #if here?
>
Ooh, it is wrong to add the '#if' here, will remove.
Thanks a lot!
Liang
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