Re: [PATCHv2 0/7] dma mapping optimisations

[Jens Axboe <axboe@kernel.dk>]

On 8/4/22 10:28 AM, Keith Busch wrote:
> On Wed, Aug 03, 2022 at 02:52:11PM -0600, Jens Axboe wrote:
>> I ran this on my test box to see how we'd do. First the bad news:
>> smaller block size IO seems slower. I ran with QD=8 and used 24 drives,
>> and using t/io_uring (with registered buffers, polled, etc) and a 512b
>> block size I get:
>>
>> IOPS=44.36M, BW=21.66GiB/s, IOS/call=1/1
>> IOPS=44.64M, BW=21.80GiB/s, IOS/call=2/2
>> IOPS=44.69M, BW=21.82GiB/s, IOS/call=1/1
>> IOPS=44.55M, BW=21.75GiB/s, IOS/call=2/2
>> IOPS=44.93M, BW=21.94GiB/s, IOS/call=1/1
>> IOPS=44.79M, BW=21.87GiB/s, IOS/call=1/2
>>
>> and adding -D1 I get:
>>
>> IOPS=43.74M, BW=21.36GiB/s, IOS/call=1/1
>> IOPS=44.04M, BW=21.50GiB/s, IOS/call=1/1
>> IOPS=43.63M, BW=21.30GiB/s, IOS/call=2/2
>> IOPS=43.67M, BW=21.32GiB/s, IOS/call=1/1
>> IOPS=43.57M, BW=21.28GiB/s, IOS/call=1/2
>> IOPS=43.53M, BW=21.25GiB/s, IOS/call=2/1
>>
>> which does regress that workload.
> 
> Bummer, I would expect -D1 to be no worse. My test isn't nearly as consistent
> as yours, so I'm having some trouble measuring. I'm only coming with a few
> micro-optimizations that might help. A diff is below on top of this series. I
> also created a branch with everything folded in here:

That seemed to do the trick! Don't pay any attention to the numbers
being slightly different than before for -D0, it's a slightly different
kernel. But same test, -d8 -s2 -c2, polled:

-D0 -B1
IOPS=45.39M, BW=22.16GiB/s, IOS/call=1/1
IOPS=46.06M, BW=22.49GiB/s, IOS/call=2/1
IOPS=45.70M, BW=22.31GiB/s, IOS/call=1/1
IOPS=45.71M, BW=22.32GiB/s, IOS/call=2/2
IOPS=45.83M, BW=22.38GiB/s, IOS/call=1/1
IOPS=45.64M, BW=22.29GiB/s, IOS/call=2/2

-D1 -B1
IOPS=45.94M, BW=22.43GiB/s, IOS/call=1/1
IOPS=46.08M, BW=22.50GiB/s, IOS/call=1/1
IOPS=46.27M, BW=22.59GiB/s, IOS/call=2/1
IOPS=45.88M, BW=22.40GiB/s, IOS/call=1/1
IOPS=46.18M, BW=22.55GiB/s, IOS/call=2/1
IOPS=46.13M, BW=22.52GiB/s, IOS/call=2/2
IOPS=46.40M, BW=22.66GiB/s, IOS/call=1/1

which is a smidge higher, and definitely not regressing now.

-- 
Jens Axboe