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Date:      Sun, 15 Apr 2007 17:10:53 -0600
From:      Scott Long <scottl@samsco.org>
To:        Nate Lawson <nate@root.org>
Cc:        cvs-src@FreeBSD.org, src-committers@FreeBSD.org, Scott Long <scottl@FreeBSD.org>, cvs-all@FreeBSD.org
Subject:   Re: cvs commit: src/sys/cam cam_ccb.h cam_periph.c cam_periph.h  cam_sim.c cam_sim.h cam_xpt.c cam_xpt.h cam_xpt_periph.h src/sys/cam/scsi scsi_cd.c scsi_ch.c scsi_da.c scsi_low.c scsi_pass.c scsi_pt.c scsi_sa.c scsi_ses.c scsi_sg.c ...
Message-ID:  <4622B0FD.9000400@samsco.org>
In-Reply-To: <462260B7.8090602@root.org>
References:  <20070415084926.C77C816A521@hub.freebsd.org> <462260B7.8090602@root.org>

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Nate Lawson wrote:
[...]
> 
> Amazing work, I owe you a beer for following through where none of us
> did.  I see you went with the SIM lock approach, which seems reasonable.

I was surprised when I measured the contention on the SIM lock.  It was 
much lower than I expected it to be.  So this approach is looking to be
pretty good.  It can be improved a little bit in CAM, but the focus will
now be on efficient locking strategies for the drivers.  I have simple
locking implementations for MPT, AHC, and AHD right now, and I'll have
CISS and maybe SYM shortly.  I suspect that the easiest approach to an
efficient strategy will be to make the driver ithreads be a lock-free as
possible.

I'm planning on writing a few pages of design docs on this in the next 
few days to give people a guide for locking down their drivers.

Scott



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