Re: [PATCH v4 01/10] sched: Provide sparsemask, a reduced contention bitmap

[Tim Chen]

On 12/6/18 1:28 PM, Steve Sistare wrote:
> Provide struct sparsemask and functions to manipulate it.  A sparsemask is
> a sparse bitmap.  It reduces cache contention vs the usual bitmap when many
> threads concurrently set, clear, and visit elements, by reducing the number
> of significant bits per cacheline.  For each cacheline chunk of the mask,
> only the first K bits of the first word are used, and the remaining bits
> are ignored, where K is a creation time parameter.  Thus a sparsemask that
> can represent a set of N elements is approximately (N/K * CACHELINE) bytes
> in size.
> 
> This type is simpler and more efficient than the struct sbitmap used by
> block drivers.
> 
> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>

Steve,

We did a test of this patch set with an OLTP benchmark using Oracle database
on a 2 socket SKX platform with 2 X 28 cores.  The patchset boosted the
performance by 3.5%.  

The percentage of cpu idle time is lowered by 5%,
with user time increased by 4% and kernel time increased by 1%,
indicating a better cpu utilization overall.

The performance looks encouraging.

Thanks.

Tim