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 --- include/block/block_int.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include/block') diff --git a/include/block/block_int.h b/include/block/block_int.h index 057d88b1fc..f1a54db0f8 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; -- cgit v1.2.3-55-g7522