On Wed, Sep 01, 2021 at 04:14:34PM +0300, Max Gurtovoy wrote: > No need to pre-allocate a big buffer for the IO SGL anymore. If a device > has lots of deep queues, preallocation for the sg list can consume > substantial amounts of memory. For HW virtio-blk device, nr_hw_queues > can be 64 or 128 and each queue's depth might be 128. This means the > resulting preallocation for the data SGLs is big. > > Switch to runtime allocation for SGL for lists longer than 2 entries. > This is the approach used by NVMe drivers so it should be reasonable for > virtio block as well. Runtime SGL allocation has always been the case > for the legacy I/O path so this is nothing new. > > The preallocated small SGL depends on SG_CHAIN so if the ARCH doesn't > support SG_CHAIN, use only runtime allocation for the SGL. > > Re-organize the setup of the IO request to fit the new sg chain > mechanism. > > No performance degradation was seen (fio libaio engine with 16 jobs and > 128 iodepth): > > IO size IOPs Rand Read (before/after) IOPs Rand Write (before/after) > -------- --------------------------------- ---------------------------------- > 512B 318K/316K 329K/325K > > 4KB 323K/321K 353K/349K > > 16KB 199K/208K 250K/275K > > 128KB 36K/36.1K 39.2K/41.7K > > Signed-off-by: Max Gurtovoy <mgurtovoy@xxxxxxxxxx> > Reviewed-by: Israel Rukshin <israelr@xxxxxxxxxx> > --- > > changes from V2: > - initialize vbr->out_hdr.sector during virtblk_setup_cmd > > changes from V1: > - Kconfig update (from Christoph) > - Re-order cmd setup (from Christoph) > - use flexible sg pointer in the cmd (from Christoph) > - added perf numbers to commit msg (from Feng Li) > > --- > drivers/block/Kconfig | 1 + > drivers/block/virtio_blk.c | 155 +++++++++++++++++++++++-------------- > 2 files changed, 100 insertions(+), 56 deletions(-) Hi Max, I can run benchmark to give everyone more confidence about this change. Should I test this version or are you still planning to make code changes? Stefan
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