Re: slub: bulk allocation from per cpu partial pages

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Fri, 17 Apr 2015 07:44:46 +0200
Jesper Dangaard Brouer <brouer@redhat.com> wrote:

> On Thu, 16 Apr 2015 10:54:07 -0500 (CDT)
> Christoph Lameter <cl@linux.com> wrote:
> 
> > On Thu, 16 Apr 2015, Jesper Dangaard Brouer wrote:
> > 
> > > On CPU E5-2630 @ 2.30GHz, the cost of kmem_cache_alloc +
> > > kmem_cache_free, is a tight loop (most optimal fast-path), cost 22ns.
> > > With elem size 256 bytes, where slab chooses to make 32 obj-per-slab.
> > >
> > > With this patch, testing different bulk sizes, the cost of alloc+free
> > > per element is improved for small sizes of bulk (which I guess this the
> > > is expected outcome).
> > >
> > > Have something to compare against, I also ran the bulk sizes through
> > > the fallback versions __kmem_cache_alloc_bulk() and
> > > __kmem_cache_free_bulk(), e.g. the none optimized versions.
> > >
> > >  size    --  optimized -- fallback
> > >  bulk  8 --  15ns      --  22ns
> > >  bulk 16 --  15ns      --  22ns
> > 
> > Good.
> > 
> > >  bulk 30 --  44ns      --  48ns
> > >  bulk 32 --  47ns      --  50ns
> > >  bulk 64 --  52ns      --  54ns
> > 
> > Hmm.... We are hittling the atomics I guess... What you got so far is only
> > using the per cpu data. Wonder how many partial pages are available
> 
> Ups, I can see that this kernel don't have CONFIG_SLUB_CPU_PARTIAL,
> I'll re-run tests with this enabled.

Results with CONFIG_SLUB_CPU_PARTIAL.

 size    --  optimized -- fallback
 bulk  8 --  16ns      -- 22ns
 bulk 16 --  16ns      -- 22ns
 bulk 30 --  16ns      -- 22ns
 bulk 32 --  16ns      -- 22ns
 bulk 64 --  30ns      -- 38ns

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

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