Re: [PATCH 3/5] migration: Introduce unimplemented 'qatzip' compression method

[Fabiano Rosas <farosas@suse.de>]

Bryan Zhang <bryan.zhang@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.zhang@bytedance.com>
> Signed-off-by: Hao Xiang <hao.xiang@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.zhang@bytedance.com>
> + *  Hao Xiang   <hao.xiang@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/ZTFCnqbbqlmsUkRC@redhat.com

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.liu@intel.com

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.