Re: [ANNOUNCE 0/6] Open-iSCSI High-Performance Initiator for Linux

From: Dmitry Yusupov
Date: Wed Mar 09 2005 - 01:29:57 EST

On Tue, 2005-03-08 at 22:05 -0800, Matt Mackall wrote:
> On Tue, Mar 08, 2005 at 09:51:39PM -0800, Alex Aizman wrote:
> > Matt Mackall wrote:
> >
> > >How big is the userspace client?
> > >
> > Hmm.. x86 executable? source?
> >
> > Anyway, there's about 12,000 lines of user space code, and growing. In
> > the kernel we have approx. 3,300 lines.
> >
> > >>- 450MB/sec Read on a single connection (2-way 2.4Ghz Opteron, 64KB block
> > >>size);
> > >
> > >With what network hardware and drives, please?
> > >
> > Neterion's 10GbE adapters. RAM disk on the target side.
> Ahh.
> Snipped my question about userspace deadlocks - that was the important
> one. It is in fact why the sfnet one is written as it is - it
> originally had a userspace component and turned out to be easy to
> deadlock under load because of it.

As Scott Ferris pointed out, the main reason for deadlock in sfnet was
blocking behavior of page cache when daemon tried to do filesystem IO,
namely syslog(). That was 2.4.x kernel. We don't know whether it is
fixed in 2.6.x. If someone knows, please let us know. Meanwhile we came
up with work-around design in user-space. "Paged out" problem fixed
already in our subversion repository by utilizing mlockall() syscall.
Also we have IMHO, working solution for OOM during ERL=0 TCP re-connect.


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