From 24b36e9813ec15da7db62e3b3621730710c5f020 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 3 Jun 2021 10:34:23 +0200 Subject: block: add max_hw_transfer to BlockLimits 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 --- block/block-backend.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'block/block-backend.c') diff --git a/block/block-backend.c b/block/block-backend.c index 6e37582..deb55c2 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1953,6 +1953,19 @@ 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) { -- cgit v1.1