From: Stefano Garzarella <sgarzare@redhat.com> To: virtualization@lists.linux-foundation.org Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>, netdev@vger.kernel.org Subject: [PATCH v2] vhost: cache avail index in vhost_enable_notify() Date: Fri, 21 Jan 2022 16:31:08 +0100 [thread overview] Message-ID: <20220121153108.187291-1-sgarzare@redhat.com> (raw) In vhost_enable_notify() we enable the notifications and we read the avail index to check if new buffers have become available in the meantime. We are not caching the avail index, so when the device will call vhost_get_vq_desc(), it will find the old value in the cache and it will read the avail index again. It would be better to refresh the cache every time we read avail index, so let's change vhost_enable_notify() caching the value in `avail_idx` and compare it with `last_avail_idx` to check if there are new buffers available. We don't expect a significant performance boost because the above path is not very common, indeed vhost_enable_notify() is often called with unlikely(), expecting that avail index has not been updated. We ran virtio-test/vhost-test and noticed minimal improvement as expected. To stress the patch more, we modified vhost_test.ko to call vhost_enable_notify()/vhost_disable_notify() on every cycle when calling vhost_get_vq_desc(); in this case we observed a more evident improvement, with a reduction of the test execution time of about 3.7%. Signed-off-by: Stefano Garzarella <sgarzare@redhat.com> --- v2 - added performance info in the commit description [MST] --- drivers/vhost/vhost.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 59edb5a1ffe2..07363dff559e 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -2543,8 +2543,9 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) &vq->avail->idx, r); return false; } + vq->avail_idx = vhost16_to_cpu(vq, avail_idx); - return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx; + return vq->avail_idx != vq->last_avail_idx; } EXPORT_SYMBOL_GPL(vhost_enable_notify); -- 2.31.1
WARNING: multiple messages have this Message-ID (diff)
From: Stefano Garzarella <sgarzare@redhat.com> To: virtualization@lists.linux-foundation.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com> Subject: [PATCH v2] vhost: cache avail index in vhost_enable_notify() Date: Fri, 21 Jan 2022 16:31:08 +0100 [thread overview] Message-ID: <20220121153108.187291-1-sgarzare@redhat.com> (raw) In vhost_enable_notify() we enable the notifications and we read the avail index to check if new buffers have become available in the meantime. We are not caching the avail index, so when the device will call vhost_get_vq_desc(), it will find the old value in the cache and it will read the avail index again. It would be better to refresh the cache every time we read avail index, so let's change vhost_enable_notify() caching the value in `avail_idx` and compare it with `last_avail_idx` to check if there are new buffers available. We don't expect a significant performance boost because the above path is not very common, indeed vhost_enable_notify() is often called with unlikely(), expecting that avail index has not been updated. We ran virtio-test/vhost-test and noticed minimal improvement as expected. To stress the patch more, we modified vhost_test.ko to call vhost_enable_notify()/vhost_disable_notify() on every cycle when calling vhost_get_vq_desc(); in this case we observed a more evident improvement, with a reduction of the test execution time of about 3.7%. Signed-off-by: Stefano Garzarella <sgarzare@redhat.com> --- v2 - added performance info in the commit description [MST] --- drivers/vhost/vhost.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 59edb5a1ffe2..07363dff559e 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -2543,8 +2543,9 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) &vq->avail->idx, r); return false; } + vq->avail_idx = vhost16_to_cpu(vq, avail_idx); - return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx; + return vq->avail_idx != vq->last_avail_idx; } EXPORT_SYMBOL_GPL(vhost_enable_notify); -- 2.31.1 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
next reply other threads:[~2022-01-21 15:31 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-01-21 15:31 Stefano Garzarella [this message] 2022-01-21 15:31 ` [PATCH v2] vhost: cache avail index in vhost_enable_notify() Stefano Garzarella
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20220121153108.187291-1-sgarzare@redhat.com \ --to=sgarzare@redhat.com \ --cc=jasowang@redhat.com \ --cc=kvm@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=mst@redhat.com \ --cc=netdev@vger.kernel.org \ --cc=virtualization@lists.linux-foundation.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.