From: "Michael S. Tsirkin" <mst@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: avi@redhat.com, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache when possible
Date: Fri, 31 Aug 2012 12:56:28 +0300 [thread overview]
Message-ID: <20120831095628.GB24244@redhat.com> (raw)
In-Reply-To: <50408587.5030603@gmail.com>
On Fri, Aug 31, 2012 at 11:36:07AM +0200, Sasha Levin wrote:
> On 08/30/2012 03:38 PM, Michael S. Tsirkin wrote:
> >> +static unsigned int indirect_alloc_thresh = 16;
> > Why 16? Please make is MAX_SG + 1 this makes some sense.
>
> Wouldn't MAX_SG mean we always allocate from the cache? Isn't the memory waste
> too big in this case?
Sorry. I really meant MAX_SKB_FRAGS + 1. MAX_SKB_FRAGS is 17 so gets us
threshold of 18. It is less than the size of an skb+shinfo itself so -
does it look too big to you? Also why do you think 16 is not too big but
18 is? If there's a reason then I am fine with 16 too but then please
put it in code comment near where the value is set.
Yes this means virtio net always allocates from cache
but this is a good thing, isn't it? Gets us more consistent
performance.
--
MST
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, avi@redhat.com,
kvm@vger.kernel.org
Subject: Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache when possible
Date: Fri, 31 Aug 2012 12:56:28 +0300 [thread overview]
Message-ID: <20120831095628.GB24244@redhat.com> (raw)
In-Reply-To: <50408587.5030603@gmail.com>
On Fri, Aug 31, 2012 at 11:36:07AM +0200, Sasha Levin wrote:
> On 08/30/2012 03:38 PM, Michael S. Tsirkin wrote:
> >> +static unsigned int indirect_alloc_thresh = 16;
> > Why 16? Please make is MAX_SG + 1 this makes some sense.
>
> Wouldn't MAX_SG mean we always allocate from the cache? Isn't the memory waste
> too big in this case?
Sorry. I really meant MAX_SKB_FRAGS + 1. MAX_SKB_FRAGS is 17 so gets us
threshold of 18. It is less than the size of an skb+shinfo itself so -
does it look too big to you? Also why do you think 16 is not too big but
18 is? If there's a reason then I am fine with 16 too but then please
put it in code comment near where the value is set.
Yes this means virtio net always allocates from cache
but this is a good thing, isn't it? Gets us more consistent
performance.
--
MST
next prev parent reply other threads:[~2012-08-31 9:56 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-30 11:21 [PATCH v3 1/2] virtio-ring: Use threshold for switching to indirect descriptors Sasha Levin
2012-08-30 11:21 ` Sasha Levin
2012-08-30 11:21 ` [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache when possible Sasha Levin
2012-08-30 11:21 ` Sasha Levin
2012-08-30 13:38 ` Michael S. Tsirkin
2012-08-30 13:38 ` Michael S. Tsirkin
2012-08-31 9:36 ` Sasha Levin
2012-08-31 9:36 ` Sasha Levin
2012-08-31 9:56 ` Michael S. Tsirkin [this message]
2012-08-31 9:56 ` Michael S. Tsirkin
2012-09-04 16:34 ` Avi Kivity
2012-09-04 16:34 ` Avi Kivity
2012-09-04 16:36 ` Avi Kivity
2012-09-04 16:36 ` Avi Kivity
2012-09-04 18:41 ` Michael S. Tsirkin
2012-09-04 18:41 ` Michael S. Tsirkin
2012-09-05 14:21 ` Avi Kivity
2012-09-05 14:21 ` Avi Kivity
2012-09-05 14:27 ` Michael S. Tsirkin
2012-09-05 14:27 ` Michael S. Tsirkin
2012-08-30 14:14 ` [PATCH v3 1/2] virtio-ring: Use threshold for switching to indirect descriptors Michael S. Tsirkin
2012-08-30 14:14 ` Michael S. Tsirkin
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