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

On Tue, Sep 04, 2012 at 07:34:19PM +0300, Avi Kivity wrote:

On 08/31/2012 12:56 PM, Michael S. Tsirkin wrote:

quoted

On Fri, Aug 31, 2012 at 11:36:07AM +0200, Sasha Levin wrote:

quoted

On 08/30/2012 03:38 PM, Michael S. Tsirkin wrote:

quoted

quoted

+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.

kmalloc() also goes to a cache.  Is there a measurable difference?

Yes see 0/2 and followup discussion.

Ugh, there's an ugly loop in __find_general_cachep(), which really wants
to be replaced with fls().

-- 
error compiling committee.c: too many arguments to function