From: Stefan Hajnoczi <stefanha@redhat.com>
To: Max Gurtovoy <mgurtovoy@nvidia.com>
Cc: hch@infradead.org, mst@redhat.com,
virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
israelr@nvidia.com, nitzanc@nvidia.com, oren@nvidia.com,
linux-block@vger.kernel.org, axboe@kernel.dk
Subject: Re: [PATCH v3 1/1] virtio-blk: avoid preallocating big SGL for data
Date: Tue, 14 Sep 2021 13:22:47 +0100 [thread overview]
Message-ID: <YUCUF7co94CRGkGU@stefanha-x1.localdomain> (raw)
In-Reply-To: <692f8e81-8585-1d39-e7a4-576ae01438a1@nvidia.com>
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On Mon, Sep 13, 2021 at 05:50:21PM +0300, Max Gurtovoy wrote:
>
> On 9/6/2021 6:09 PM, Stefan Hajnoczi wrote:
> > 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
> > I ran fio randread benchmarks with 4k, 16k, 64k, and 128k at iodepth 1,
> > 8, and 64 on two vCPUs. The results look fine, there is no significant
> > regression.
> >
> > iodepth=1 and iodepth=64 are very consistent. For some reason the
> > iodepth=8 has significant variance but I don't think it's the fault of
> > this patch.
> >
> > Fio results and the Jupyter notebook export are available here (check
> > out benchmark.html to see the graphs):
> >
> > https://gitlab.com/stefanha/virt-playbooks/-/tree/virtio-blk-sgl-allocation-benchmark/notebook
> >
> > Guest:
> > - Fedora 34
> > - Linux v5.14
> > - 2 vCPUs (pinned), 4 GB RAM (single host NUMA node)
> > - 1 IOThread (pinned)
> > - virtio-blk aio=native,cache=none,format=raw
> > - QEMU 6.1.0
> >
> > Host:
> > - RHEL 8.3
> > - Linux 4.18.0-240.22.1.el8_3.x86_64
> > - Intel(R) Xeon(R) Silver 4214 CPU @ 2.20GHz
> > - Intel Optane DC P4800X
> >
> > Stefan
>
> Thanks, Stefan.
>
> Would you like me to add some of the results in my commit msg ? or Tested-By
> sign ?
Thanks, there's no need to change the commit description.
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Stefan Hajnoczi <stefanha@redhat.com>
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next prev parent reply other threads:[~2021-09-14 12:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 13:14 [PATCH v3 1/1] virtio-blk: avoid preallocating big SGL for data Max Gurtovoy
2021-09-01 14:50 ` Michael S. Tsirkin
2021-09-01 14:58 ` Max Gurtovoy
2021-09-01 15:27 ` Jens Axboe
2021-09-01 22:25 ` Max Gurtovoy
2021-09-02 2:08 ` Jens Axboe
2021-09-02 12:21 ` Stefan Hajnoczi
2021-09-02 12:41 ` Max Gurtovoy
2021-09-06 15:09 ` Stefan Hajnoczi
2021-09-10 6:32 ` Feng Li
2021-09-13 14:50 ` Max Gurtovoy
2021-09-14 12:22 ` Stefan Hajnoczi [this message]
2021-09-23 13:40 ` Max Gurtovoy
2021-09-23 15:37 ` Michael S. Tsirkin
2021-10-22 9:15 ` Michael S. Tsirkin
2021-10-24 14:31 ` Max Gurtovoy
2021-09-27 11:59 ` Christoph Hellwig
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