Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cachewhen possible

[Michael S. Tsirkin]

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.



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MST
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