[stgt] [PATCH RFC v2] tgtd: send/recv iSCSI PDUs in worker threads

[Hitoshi Mitake]

At Sun, 17 Nov 2013 22:50:58 +0900 (JST),
FUJITA Tomonori wrote:
> 
> On Sun, 10 Nov 2013 17:49:07 +0900
> Hitoshi Mitake <mitake.hitoshi at gmail.com> wrote:
> 
> > From: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> > 
> > Current tgtd sends and receives iSCSI PDUs in its main event
> > loop. This design can cause bottleneck when many iSCSI clients connect
> > to single tgtd process. For example, we need multiple tgtd processes
> > for utilizing fast network like 10 GbE because typical single
> > processor core isn't fast enough for processing bunch of requests.
> > 
> > This patch lets tgtd send/receive iSCSI PDUs and check digests in its
> > worker threads. After applying this patch, the bottleneck in the main
> > event loop is removed and the performance is improved.
> > 
> > The improvement can be seen even if tgtd and iSCSI initiator are
> > running on a single host. Below is a snippet of fio result on my
> > laptop. The workload is 128MB random RW. Backingstore is sheepdog.
> > 
> > Original tgtd:
> >   read : io=65392KB, bw=4445.2KB/s, iops=1111, runt= 14711msec
> >   write: io=65680KB, bw=4464.8KB/s, iops=1116, runt= 14711msec
> > 
> > tgtd with this patch:
> >   read : io=65392KB, bw=5098.9KB/s, iops=1274, runt= 12825msec
> >   write: io=65680KB, bw=5121.3KB/s, iops=1280, runt= 12825msec
> 
> Can you check how this scales with tcp connections on a
> reasonably-high-performance server?

Sure. I'd like to evaluate and post a result in the near future.

Thanks,
Hitoshi
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