From 6773549977d94c504ec76aed67506ae85adff973 Mon Sep 17 00:00:00 2001

From: Paolo Bonzini <pbonzini@redhat.com>

Date: Fri, 16 Jul 2021 16:51:33 -0400

Subject: [PATCH 17/43] block: add max_hw_transfer to BlockLimits

RH-Author: Miroslav Rezanina <mrezanin@redhat.com>

RH-Bugzilla: 1957194

For block host devices, I/O can happen through either the kernel file

descriptor I/O system calls (preadv/pwritev, io_submit, io_uring)

or the SCSI passthrough ioctl SG_IO.

In the latter case, the size of each transfer can be limited by the

HBA, while for file descriptor I/O the kernel is able to split and

merge I/O in smaller pieces as needed.  Applying the HBA limits to

file descriptor I/O results in more system calls and suboptimal

performance, so this patch splits the max_transfer limit in two:

max_transfer remains valid and is used in general, while max_hw_transfer

is limited to the maximum hardware size.  max_hw_transfer can then be

included by the scsi-generic driver in the block limits page, to ensure

that the stricter hardware limit is used.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

(cherry picked from commit 24b36e9813ec15da7db62e3b3621730710c5f020)

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block/block-backend.c          | 13 +++++++++++++

 block/file-posix.c             |  2 +-

 block/io.c                     |  2 ++

 hw/scsi/scsi-generic.c         |  2 +-

 include/block/block_int.h      |  7 +++++++

 include/sysemu/block-backend.h |  1 +

 6 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c

index 136cc602c5..b5f5b4b048 100644

--- a/block/block-backend.c

+++ b/block/block-backend.c

@@ -1939,6 +1939,19 @@ uint32_t blk_get_request_alignment(BlockBackend *blk)

     return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE;

 }

+/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */

+uint64_t blk_get_max_hw_transfer(BlockBackend *blk)

+{

+    BlockDriverState *bs = blk_bs(blk);

+    uint64_t max = INT_MAX;

+

+    if (bs) {

+        max = MIN_NON_ZERO(max, bs->bl.max_hw_transfer);

+        max = MIN_NON_ZERO(max, bs->bl.max_transfer);

+    }

+    return ROUND_DOWN(max, blk_get_request_alignment(blk));

+}

+

 /* Returns the maximum transfer length, in bytes; guaranteed nonzero */

 uint32_t blk_get_max_transfer(BlockBackend *blk)

 {

diff --git a/block/file-posix.c b/block/file-posix.c

index 1a6c799e19..44325a635d 100644

--- a/block/file-posix.c

+++ b/block/file-posix.c

@@ -1258,7 +1258,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)

         int ret = sg_get_max_transfer_length(s->fd);

         if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {

-            bs->bl.max_transfer = pow2floor(ret);

+            bs->bl.max_hw_transfer = pow2floor(ret);

         }

         ret = sg_get_max_segments(s->fd);

diff --git a/block/io.c b/block/io.c

index ca2dca3007..a4b2e3adf1 100644

--- a/block/io.c

+++ b/block/io.c

@@ -126,6 +126,8 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src)

 {

     dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer);

     dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer);

+    dst->max_hw_transfer = MIN_NON_ZERO(dst->max_hw_transfer,

+                                        src->max_hw_transfer);

     dst->opt_mem_alignment = MAX(dst->opt_mem_alignment,

                                  src->opt_mem_alignment);

     dst->min_mem_alignment = MAX(dst->min_mem_alignment,

diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c

index 82e1e2ee79..3762dce749 100644

--- a/hw/scsi/scsi-generic.c

+++ b/hw/scsi/scsi-generic.c

@@ -179,7 +179,7 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s)

         (r->req.cmd.buf[1] & 0x01)) {

         page = r->req.cmd.buf[2];

         if (page == 0xb0) {

-            uint32_t max_transfer = blk_get_max_transfer(s->conf.blk);

+            uint64_t max_transfer = blk_get_max_hw_transfer(s->conf.blk);

             uint32_t max_iov = blk_get_max_iov(s->conf.blk);

             assert(max_transfer);

diff --git a/include/block/block_int.h b/include/block/block_int.h

index 88e4111939..09d8630ec4 100644

--- a/include/block/block_int.h

+++ b/include/block/block_int.h

@@ -695,6 +695,13 @@ typedef struct BlockLimits {

      * clamped down. */

     uint32_t max_transfer;

+    /* Maximal hardware transfer length in bytes.  Applies whenever

+     * transfers to the device bypass the kernel I/O scheduler, for

+     * example with SG_IO.  If larger than max_transfer or if zero,

+     * blk_get_max_hw_transfer will fall back to max_transfer.

+     */

+    uint64_t max_hw_transfer;

+

     /* memory alignment, in bytes so that no bounce buffer is needed */

     size_t min_mem_alignment;

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h

index 5423e3d9c6..9ac5f7bbd3 100644

--- a/include/sysemu/block-backend.h

+++ b/include/sysemu/block-backend.h

@@ -208,6 +208,7 @@ void blk_eject(BlockBackend *blk, bool eject_flag);

 int blk_get_flags(BlockBackend *blk);

 uint32_t blk_get_request_alignment(BlockBackend *blk);

 uint32_t blk_get_max_transfer(BlockBackend *blk);

+uint64_t blk_get_max_hw_transfer(BlockBackend *blk);

 int blk_get_max_iov(BlockBackend *blk);

 void blk_set_guest_block_size(BlockBackend *blk, int align);

 void *blk_try_blockalign(BlockBackend *blk, size_t size);

-- 

2.27.0