> -----Original Message-----
> From: Fabiano Rosas <faro...@suse.de>
> Sent: Tuesday, January 9, 2024 4:28 AM
> To: Liu, Yuan1 <yuan1....@intel.com>; Hao Xiang <hao.xi...@bytedance.com>
> Cc: Bryan Zhang <bryan.zh...@bytedance.com>; qemu-devel@nongnu.org;
> marcandre.lur...@redhat.com; pet...@redhat.com; quint...@redhat.com;
> peter.mayd...@linaro.org; berra...@redhat.com
> Subject: RE: [External] Re: [PATCH 3/5] migration: Introduce unimplemented
> 'qatzip' compression method
>
> "Liu, Yuan1" <yuan1....@intel.com> writes:
>
> >> -----Original Message-----
> >> From: Hao Xiang <hao.xi...@bytedance.com>
> >> Sent: Saturday, January 6, 2024 7:53 AM
> >> To: Fabiano Rosas <faro...@suse.de>
> >> Cc: Bryan Zhang <bryan.zh...@bytedance.com>; qemu-devel@nongnu.org;
> >> marcandre.lur...@redhat.com; pet...@redhat.com; quint...@redhat.com;
> >> peter.mayd...@linaro.org; Liu, Yuan1 <yuan1....@intel.com>;
> >> berra...@redhat.com
> >> Subject: Re: [External] Re: [PATCH 3/5] migration: Introduce
> >> unimplemented 'qatzip' compression method
> >>
> >> On Fri, Jan 5, 2024 at 12:07 PM Fabiano Rosas <faro...@suse.de> wrote:
> >> >
> >> > Bryan Zhang <bryan.zh...@bytedance.com> writes:
> >> >
> >> > +cc Yuan Liu, Daniel Berrangé
> >> >
> >> > > Adds support for 'qatzip' as an option for the multifd
> >> > > compression method parameter, but copy-pastes the no-op logic to
> >> > > leave the actual methods effectively unimplemented. This is in
> >> > > preparation of a subsequent commit that will implement actually
> >> > > using QAT for compression and decompression.
> >> > >
> >> > > Signed-off-by: Bryan Zhang <bryan.zh...@bytedance.com>
> >> > > Signed-off-by: Hao Xiang <hao.xi...@bytedance.com>
> >> > > ---
> >> > > hw/core/qdev-properties-system.c | 6 ++-
> >> > > migration/meson.build | 1 +
> >> > > migration/multifd-qatzip.c | 81
> >> ++++++++++++++++++++++++++++++++
> >> > > migration/multifd.h | 1 +
> >> > > qapi/migration.json | 5 +-
> >> > > 5 files changed, 92 insertions(+), 2 deletions(-) create mode
> >> > > 100644 migration/multifd-qatzip.c
> >> > >
> >> > > diff --git a/hw/core/qdev-properties-system.c
> >> > > b/hw/core/qdev-properties-system.c
> >> > > index 1a396521d5..d8e48dcb0e 100644
> >> > > --- a/hw/core/qdev-properties-system.c
> >> > > +++ b/hw/core/qdev-properties-system.c
> >> > > @@ -658,7 +658,11 @@ const PropertyInfo qdev_prop_fdc_drive_type
> >> > > = { const PropertyInfo qdev_prop_multifd_compression = {
> >> > > .name = "MultiFDCompression",
> >> > > .description = "multifd_compression values, "
> >> > > - "none/zlib/zstd",
> >> > > + "none/zlib/zstd"
> >> > > +#ifdef CONFIG_QATZIP
> >> > > + "/qatzip"
> >> > > +#endif
> >> > > + ,
> >> > > .enum_table = &MultiFDCompression_lookup,
> >> > > .get = qdev_propinfo_get_enum,
> >> > > .set = qdev_propinfo_set_enum, diff --git
> >> > > a/migration/meson.build b/migration/meson.build index
> >> > > 92b1cc4297..e20f318379 100644
> >> > > --- a/migration/meson.build
> >> > > +++ b/migration/meson.build
> >> > > @@ -40,6 +40,7 @@ if get_option('live_block_migration').allowed()
> >> > > system_ss.add(files('block.c')) endif
> >> > > system_ss.add(when: zstd, if_true: files('multifd-zstd.c'))
> >> > > +system_ss.add(when: qatzip, if_true: files('multifd-qatzip.c'))
> >> > >
> >> > > specific_ss.add(when: 'CONFIG_SYSTEM_ONLY',
> >> > > if_true: files('ram.c', diff --git
> >> > > a/migration/multifd-qatzip.c b/migration/multifd-qatzip.c new file
> >> > > mode 100644 index 0000000000..1733bbddb7
> >> > > --- /dev/null
> >> > > +++ b/migration/multifd-qatzip.c
> >> > > @@ -0,0 +1,81 @@
> >> > > +/*
> >> > > + * Multifd QATzip compression implementation
> >> > > + *
> >> > > + * Copyright (c) Bytedance
> >> > > + *
> >> > > + * Authors:
> >> > > + * Bryan Zhang <bryan.zh...@bytedance.com>
> >> > > + * Hao Xiang <hao.xi...@bytedance.com>
> >> > > + *
> >> > > + * This work is licensed under the terms of the GNU GPL, version 2
> or
> >> later.
> >> > > + * See the COPYING file in the top-level directory.
> >> > > + */
> >> > > +
> >> > > +#include "qemu/osdep.h"
> >> > > +#include "exec/ramblock.h"
> >> > > +#include "exec/target_page.h"
> >> > > +#include "qapi/error.h"
> >> > > +#include "migration.h"
> >> > > +#include "options.h"
> >> > > +#include "multifd.h"
> >> > > +
> >> > > +static int qatzip_send_setup(MultiFDSendParams *p, Error **errp) {
> >> > > + return 0;
> >> > > +}
> >> > > +
> >> > > +static void qatzip_send_cleanup(MultiFDSendParams *p, Error
> **errp)
> >> > > +{};
> >> > > +
> >> > > +static int qatzip_send_prepare(MultiFDSendParams *p, Error **errp)
> >> > > +{
> >> > > + MultiFDPages_t *pages = p->pages;
> >> > > +
> >> > > + for (int i = 0; i < p->normal_num; i++) {
> >> > > + p->iov[p->iovs_num].iov_base = pages->block->host + p-
> >> >normal[i];
> >> > > + p->iov[p->iovs_num].iov_len = p->page_size;
> >> > > + p->iovs_num++;
> >> > > + }
> >> > > +
> >> > > + p->next_packet_size = p->normal_num * p->page_size;
> >> > > + p->flags |= MULTIFD_FLAG_NOCOMP;
> >> > > + return 0;
> >> > > +}
> >> > > +
> >> > > +static int qatzip_recv_setup(MultiFDRecvParams *p, Error **errp) {
> >> > > + return 0;
> >> > > +}
> >> > > +
> >> > > +static void qatzip_recv_cleanup(MultiFDRecvParams *p) {};
> >> > > +
> >> > > +static int qatzip_recv_pages(MultiFDRecvParams *p, Error **errp) {
> >> > > + uint32_t flags = p->flags & MULTIFD_FLAG_COMPRESSION_MASK;
> >> > > +
> >> > > + if (flags != MULTIFD_FLAG_NOCOMP) {
> >> > > + error_setg(errp, "multifd %u: flags received %x flags
> >> expected %x",
> >> > > + p->id, flags, MULTIFD_FLAG_NOCOMP);
> >> > > + return -1;
> >> > > + }
> >> > > + for (int i = 0; i < p->normal_num; i++) {
> >> > > + p->iov[i].iov_base = p->host + p->normal[i];
> >> > > + p->iov[i].iov_len = p->page_size;
> >> > > + }
> >> > > + return qio_channel_readv_all(p->c, p->iov, p->normal_num,
> >> > > +errp); }
> >> > > +
> >> > > +static MultiFDMethods multifd_qatzip_ops = {
> >> > > + .send_setup = qatzip_send_setup,
> >> > > + .send_cleanup = qatzip_send_cleanup,
> >> > > + .send_prepare = qatzip_send_prepare,
> >> > > + .recv_setup = qatzip_recv_setup,
> >> > > + .recv_cleanup = qatzip_recv_cleanup,
> >> > > + .recv_pages = qatzip_recv_pages };
> >> > > +
> >> > > +static void multifd_qatzip_register(void) {
> >> > > + multifd_register_ops(MULTIFD_COMPRESSION_QATZIP,
> >> > > +&multifd_qatzip_ops); }
> >> > > +
> >> > > +migration_init(multifd_qatzip_register);
> >> > > diff --git a/migration/multifd.h b/migration/multifd.h index
> >> > > a835643b48..5600f7fc82 100644
> >> > > --- a/migration/multifd.h
> >> > > +++ b/migration/multifd.h
> >> > > @@ -33,6 +33,7 @@ int multifd_queue_page(QEMUFile *f, RAMBlock
> >> > > *block, ram_addr_t offset); #define MULTIFD_FLAG_NOCOMP (0 << 1)
> >> > > #define MULTIFD_FLAG_ZLIB (1 << 1) #define MULTIFD_FLAG_ZSTD (2 <<
> >> > > 1)
> >> > > +#define MULTIFD_FLAG_QATZIP (3 << 1)
> >> > >
> >> > > /* This value needs to be a multiple of qemu_target_page_size() */
> >> > > #define MULTIFD_PACKET_SIZE (512 * 1024) diff --git
> >> > > a/qapi/migration.json b/qapi/migration.json index
> >> > > 6d5a4b0489..e3cc195aed 100644
> >> > > --- a/qapi/migration.json
> >> > > +++ b/qapi/migration.json
> >> > > @@ -625,11 +625,14 @@
> >> > > #
> >> > > # @zstd: use zstd compression method.
> >> > > #
> >> > > +# @qatzip: use qatzip compression method.
> >> > > +#
> >> > > # Since: 5.0
> >> > > ##
> >> > > { 'enum': 'MultiFDCompression',
> >> > > 'data': [ 'none', 'zlib',
> >> > > - { 'name': 'zstd', 'if': 'CONFIG_ZSTD' } ] }
> >> > > + { 'name': 'zstd', 'if': 'CONFIG_ZSTD' },
> >> > > + { 'name': 'qatzip', 'if': 'CONFIG_QATZIP'} ] }
> >> >
> >> > In another thread adding support to another Intel accelerator (IAA)
> we
> >> > decided that it was better to select the offloading as an accelerator
> >> > method to multifd zlib rather than as an entirely new compression
> >> > format. Take a look at that discussion:
> >> > https://lore.kernel.org/r/ztfcnqbbqlmsu...@redhat.com
> >>
> >> We had some early discussion with Intel folks (probably a different
> team
> >> than the one with the above patchset). The understanding at the time is
> >> that QAT is good at both bulk data compression and decompression. IAA
> is
> >> good at decompression with smaller data size but compression
> performance
> >> is not the best. In multifd, we are compressing up to 128 4k pages at a
> >> time and potentially this can increase by configuring the packet size,
> at
> >> the time we thought QAT could be a better fit in the multifd live
> >> migration scenario. We would like to hear more from Intel.
> >>
> >> From our benchmark testing, with two QAT devices, we can get deflate
> >> compression throughout to around 7GB/s with ~160% CPU. That's beating
> the
> >> current software implementation (zlib and zstd) by a lot. We are still
> >> tuning the configuration in QEMU live migration now.
> >>
> >> >
> >> > As I understand it, QAT + QATzip would be compatible with both zlib
> >> > and IAA + QPL, so we'd add another accelerator method like this:
> >> >
> >> > https://lore.kernel.org/r/20240103112851.908082-3-yuan1....@intel.com
> >> >
> >>
> >> I quickly read over the IAA patchset and I saw this:
> >>
> >> "However, due to some reasons, QPL is currently not compatible with the
> >> existing Zlib method that Zlib compressed data can be decompressed by
> QPl
> >> and vice versa."
> >>
> >> The above probably means the current zlib software implementation and
> IAA
> >> are not compatible.
> >>
> >> For QAT, although, both Intel's QATzip and zlib are internally using
> >> deflate, QATzip only supports deflate with a 4 byte header, deflate
> >> wrapped by Gzip header and footer, or deflate wrapped by Intel® QAT
> >> Gzip* extension header and footer. None of the headers can be
> recognized
> >> by zlib software implementation is my understanding. So if we want to
> make
> >> them compatible with zlib, the QATzip library needs to support that.
> >
> > The QPL library currently cannot support the Z_SYNC_FLULSH operation of
> zlib steaming.
> > This is the reason why it is not compatible with zlib.
> >
>
> I had understood from previous discussion that we'd be able to at least
> support compression with QPL and decompression with the existing
> zlib-based code. Is that not correct? I was about to suggest
> experimenting with the window size in the existing code to hopefully
> solve the 4kb window size issue. If there are other limitations, then
> that will not be enough.
>
> Also, can you point to the source of that statement about Z_SYNC_FLUSH,
> I couldn't find more information about it in the documentation.
static int zlib_send_prepare(MultiFDSendParams *p, Error **errp)
{
struct zlib_data *z = p->data;
z_stream *zs = &z->zs;
…
for (i = 0; i < p->normal_num; i++) {
uint32_t available = z->zbuff_len - out_size;
int flush = Z_NO_FLUSH;
if (i == p->normal_num - 1) {
flush = Z_SYNC_FLUSH;
}
If I understand correctly, the current implementation of multifd zlib treats
each multifd thread as a separate stream. This implementation adds zlib headers
and footers only to the beginning and end of the data, and the data transmitted
in between does not require headers and footers.
The current implementation for IAA supports compressing data indicated by
p->normal_num as a single stream. Each compressed data segment has zlib headers
and footers. Since Z_SYNC_FLUSH is not supported, this means IAA has to
complete the compression for a stream at once and cannot output parts of a
stream in advance. Therefore, the current IAA is not compatible with existing
zlib. Currently, it seems that the QAT implementation follows a similar
approach.
Regarding the reference to Z_SYNC_FLUSH, you can find it at
https://www.zlib.net/manual.html:
“If the parameter flush is set to Z_SYNC_FLUSH, all pending output is flushed
to the output buffer and the output is aligned on a byte boundary, so that the
decompressor can get all input data available so far. (In particular avail_in
is zero after the call if enough output space has been provided before the
call.) Flushing may degrade compression for some compression algorithms and so
it should be used only when necessary. This completes the current deflate block
and follows it with an empty stored block that is three bits plus filler bits
to the next byte, followed by four bytes (00 00 ff ff).”
Based on the information above, I suggest the following options:
1. Modify multifd zlib to perform stream compression each time with
p->normal_num pages. If this modification makes IAA compatible with zlib, I
will implement it in the next version as per
https://lore.kernel.org/all/20240103112851.908082-4-yuan1....@intel.com/T/ and
provide performance data. We will also verify the feasibility with QAT.
2. Use zlib compression without stream compression, meaning each page is
independently compressed. The advantage is that accelerators can concurrently
process more pages, and the current IAA and QAT can both be compatible. The
downside is a loss in compression ratio, and the length of the data after
compressing each page needs to be added to MultiFDPacket_t. If future
compression functionality considers support only on accelerators, the
compression ratio can be improved through compression levels or other features
without additional host CPU overhead.
Additionally, the default window size is set to 4K, which should effectively
support IAA hardware.
> >> > All that, of course, assuming we even want to support both
> >> > accelerators. They're addressing the same problem after all. I wonder
> >> > how we'd choose a precedence, since both seem to be present in the
> >> > same processor family.
> >> >
> >> >
> >>
> >> That's an interesting question :-) I think overall performance
> (throughput
> >> and CPU overhead) should both be considered. IAA and QAT accelerators
> >> don't present on all systems. We Bytedance choose to have both on our
> >> platform when purchasing from Intel.
