[Stgt-devel] sg_turs on stgt iscsi drive is very slow

[Ming Zhang]

On Tue, 2006-12-12 at 08:21 +0900, FUJITA Tomonori wrote:
> From: Ming Zhang <blackmagic02881 at gmail.com>
> Subject: Re: [Stgt-devel] sg_turs on stgt iscsi drive is very slow
> Date: Mon, 11 Dec 2006 18:18:06 -0500
> 
> > On Tue, 2006-12-12 at 08:02 +0900, FUJITA Tomonori wrote:
> > > From: Ming Zhang <blackmagic02881 at gmail.com>
> > > Subject: [Stgt-devel] sg_turs on stgt iscsi drive is very slow
> > > Date: Mon, 11 Dec 2006 11:58:27 -0500
> > > 
> > > > Pulled out the linux-2.6-target git tree, compiled stgt and iet under
> > > > same kernel. Export a 4 disk raid0 device to ini. Ini is open-iscsi
> > > > r598.
> > > > 
> > > > Want to know how efficient stgt handle context switch. 
> > > > 
> > > > run  sg_turs -t -n=10000 /dev/sg0 on IET drive. results is 2521/sec.
> > > 
> > > With IET, several threads handle TUR. With stgt, the single thread
> > > handles TUR (synchronously). stgt asynchronously handles only I/O
> > > commands (READ, WRITE, etc), which are expected to be performed
> > > efficiently.
> > 
> > if i set Wthreads to 1 and "ps axu" to double check there is only 1
> > worker thread, i still get 5470 op/sec.
> > 
> > also when run stgt, the top show almost no cpu activity. 
> 
> With that configuration, IET still uses three threads (two network
> threads and worker thread).

could u roughly explain a code flow of stgt for a TUR? why I see no cpu
utilization during stgt run? for iet, i saw 4-5% cpu utilization so i
know it is working. but for stgt i can not see any from top or vmstat.

> 
> 
> > > So I don't think the results are related with context switch at all.
> > 
> > ok, it is not related to CS. but then why stgt is so slow?
> > 
> > it should be easy to reproduce this at u side. if u can not reproduce
> > this slowness, i will check my environment again. i clone u git tress
> > just yesterday.
> 
> Please do real workload tests. If stgt is slow with such workloads,
> I'll dig into it. Thanks.

i tried simple dd read from iscsi drive and only give me 30MB/s. but i
forgot if i disable the debug or not. i will run it again and report.