From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: Nir Soffer <nsoffer@redhat.com>, qemu-stable@nongnu.org
Subject: Re: [PATCH 2/6] virtio-scsi: don't waste CPU polling the event virtqueue
Date: Fri, 29 Apr 2022 01:17:05 +0200 [thread overview]
Message-ID: <ca28d5bf-5bd6-e002-c420-ed9b98989555@redhat.com> (raw)
In-Reply-To: <20220427143541.119567-3-stefanha@redhat.com>
On 4/27/22 16:35, Stefan Hajnoczi wrote:
> This is typical for rx virtqueues where the device uses buffers when
> some event occurs (e.g. a packet is received, an error condition
> happens, etc).
>
> Polling non-empty virtqueues wastes CPU cycles. We are not waiting for
> new buffers to become available, we are waiting for an event to occur,
> so it's a misuse of CPU resources to poll for buffers.
Shouldn't polling wait for _used_ buffers, rather than available ones?
I agree that it's generally useless to poll the event queue, but not
because it doesn't empty the virtqueue.
Paolo
next prev parent reply other threads:[~2022-04-28 23:18 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-27 14:35 [PATCH 0/6] virtio-scsi: fix 100% CPU consumption in IOThread Stefan Hajnoczi
2022-04-27 14:35 ` [PATCH 1/6] virtio-scsi: fix ctrl and event handler functions in dataplane mode Stefan Hajnoczi
2022-04-27 19:47 ` Michael Tokarev
2022-04-28 9:05 ` Stefan Hajnoczi
2022-04-28 23:18 ` Paolo Bonzini
2022-04-27 14:35 ` [PATCH 2/6] virtio-scsi: don't waste CPU polling the event virtqueue Stefan Hajnoczi
2022-04-27 20:12 ` Nir Soffer
2022-04-28 9:05 ` Stefan Hajnoczi
2022-04-28 23:17 ` Paolo Bonzini [this message]
2022-04-30 5:52 ` Stefan Hajnoczi
2022-04-27 14:35 ` [PATCH 3/6] virtio-scsi: clean up virtio_scsi_handle_event_vq() Stefan Hajnoczi
2022-04-28 23:17 ` Paolo Bonzini
2022-04-27 14:35 ` [PATCH 4/6] virtio-scsi: clean up virtio_scsi_handle_ctrl_vq() Stefan Hajnoczi
2022-04-28 23:17 ` Paolo Bonzini
2022-04-27 14:35 ` [PATCH 5/6] virtio-scsi: clean up virtio_scsi_handle_cmd_vq() Stefan Hajnoczi
2022-04-28 23:17 ` Paolo Bonzini
2022-04-27 14:35 ` [PATCH 6/6] virtio-scsi: move request-related items from .h to .c Stefan Hajnoczi
2022-04-28 23:17 ` Paolo Bonzini
2022-05-09 9:45 ` [PATCH 0/6] virtio-scsi: fix 100% CPU consumption in IOThread Stefan Hajnoczi
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