On Wed, 2013-11-06 at 10:54 -0500, Neil Horman wrote:
> On Wed, Nov 06, 2013 at 10:34:29AM -0500, Dave Jones wrote:
> > On Wed, Nov 06, 2013 at 10:23:19AM -0500, Neil Horman wrote:
> > > do_csum was identified via perf recently as a hot spot when doing
> > > receive on ip over infiniband workloads. After alot of testing and
> > > ideas, we found the best optimization available to us currently is to
> > > prefetch the entire data buffer prior to doing the checksum
[]
> I'll fix this up and send a v3, but I'll give it a day in case there are more
> comments first.
Perhaps a reduction in prefetch loop count helps.
Was capping the amount prefetched and letting the
hardware prefetch also tested?
prefetch_lines(buff, min(len, cache_line_size() * 8u));
Also pedantry/trivial comments:
__always_inline instead of inline
static __always_inline void prefetch_lines(const void *addr, size_t len)
{
const void *end = addr + len;
...
buff doesn't need a void * cast in prefetch_lines
Beside the commit message, the comment above prefetch_lines
also needs updating to remove the "Manual Prefetching" line.
/*
* Do a 64-bit checksum on an arbitrary memory area.
* Returns a 32bit checksum.
*
* This isn't as time critical as it used to be because many NICs
* do hardware checksumming these days.
*
* Things tried and found to not make it faster:
* Manual Prefetching
* Unrolling to an 128 bytes inner loop.
*/
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