From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@canonical.com>, linux-kernel@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH] block: virtio_blk: don't hold spin lock during world switch
Date: Thu, 29 May 2014 21:19:14 -0600 [thread overview]
Message-ID: <5387F8B2.1070509@kernel.dk> (raw)
In-Reply-To: <1401418169-3361-1-git-send-email-ming.lei@canonical.com>
On 2014-05-29 20:49, Ming Lei wrote:
> Firstly, it isn't necessary to hold lock of vblk->vq_lock
> when notifying hypervisor about queued I/O.
>
> Secondly, virtqueue_notify() will cause world switch and
> it may take long time on some hypervisors(such as, qemu-arm),
> so it isn't good to hold the lock and block other vCPUs.
>
> On arm64 quad core VM(qemu-kvm), the patch can increase I/O
> performance a lot with VIRTIO_RING_F_EVENT_IDX enabled:
> - without the patch: 14K IOPS
> - with the patch: 34K IOPS
Patch looks good to me. I don't see a hit on my qemu-kvm testing, but it
definitely makes sense and I can see it hurting in other places.
--
Jens Axboe
WARNING: multiple messages have this Message-ID (diff)
From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@canonical.com>, linux-kernel@vger.kernel.org
Cc: Rusty Russell <rusty@rustcorp.com.au>,
"Michael S. Tsirkin" <mst@redhat.com>,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] block: virtio_blk: don't hold spin lock during world switch
Date: Thu, 29 May 2014 21:19:14 -0600 [thread overview]
Message-ID: <5387F8B2.1070509@kernel.dk> (raw)
In-Reply-To: <1401418169-3361-1-git-send-email-ming.lei@canonical.com>
On 2014-05-29 20:49, Ming Lei wrote:
> Firstly, it isn't necessary to hold lock of vblk->vq_lock
> when notifying hypervisor about queued I/O.
>
> Secondly, virtqueue_notify() will cause world switch and
> it may take long time on some hypervisors(such as, qemu-arm),
> so it isn't good to hold the lock and block other vCPUs.
>
> On arm64 quad core VM(qemu-kvm), the patch can increase I/O
> performance a lot with VIRTIO_RING_F_EVENT_IDX enabled:
> - without the patch: 14K IOPS
> - with the patch: 34K IOPS
Patch looks good to me. I don't see a hit on my qemu-kvm testing, but it
definitely makes sense and I can see it hurting in other places.
--
Jens Axboe
next prev parent reply other threads:[~2014-05-30 3:19 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-30 2:49 [PATCH] block: virtio_blk: don't hold spin lock during world switch Ming Lei
2014-05-30 3:19 ` Jens Axboe [this message]
2014-05-30 3:19 ` Jens Axboe
2014-05-30 3:34 ` Ming Lei
2014-05-30 3:35 ` Jens Axboe
2014-05-30 3:35 ` Jens Axboe
2014-05-30 5:58 ` Ming Lei
2014-05-30 5:58 ` Ming Lei
2014-05-30 6:10 ` Rusty Russell
2014-05-30 6:10 ` Rusty Russell
2014-05-30 13:52 ` Jens Axboe
2014-05-30 13:52 ` Jens Axboe
2014-06-02 1:23 ` Rusty Russell
2014-06-02 1:23 ` Rusty Russell
2014-06-02 13:06 ` Ming Lei
2014-06-02 13:06 ` Ming Lei
2014-06-11 14:44 ` Paolo Bonzini
2014-06-11 14:44 ` Paolo Bonzini
2014-06-02 14:15 ` Jens Axboe
2014-06-02 14:15 ` Jens Axboe
2014-05-30 3:34 ` Ming Lei
2014-05-30 6:05 ` Rusty Russell
2014-05-30 6:05 ` Rusty Russell
2014-05-30 15:27 ` Michael S. Tsirkin
2014-05-30 15:27 ` Michael S. Tsirkin
-- strict thread matches above, loose matches on Subject: below --
2014-05-30 2:49 Ming Lei
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