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Message-ID: <47492064.7080108@freebsd.org>
Date: Sat, 24 Nov 2007 23:12:36 -0800
From: Darren Reed <darrenr@freebsd.org>
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To: Stephan Uphoff <ups@FreeBSD.org>
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Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/share/man/man9 locking.9 rmlock.9 src/sys/conf
 files src/sys/kern kern_rmlock.c subr_lock.c subr_pcpu.c        
 subr_smp.c src/sys/sys _rmlock.h lock.h pcpu.h rmlock.h smp.h
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Stephan Uphoff wrote:
> ups         2007-11-08 14:47:55 UTC
>
>   FreeBSD src repository
>
>   Modified files:
>     share/man/man9       locking.9 
>     sys/conf             files 
>     sys/kern             subr_lock.c subr_pcpu.c subr_smp.c 
>     sys/sys              lock.h pcpu.h smp.h 
>   Added files:
>     share/man/man9       rmlock.9 
>     sys/kern             kern_rmlock.c 
>     sys/sys              _rmlock.h rmlock.h 
>   Log:
>   Initial checkin for rmlock (read mostly lock) a multi reader single writer
>   lock optimized for almost exclusive reader access. (see also rmlock.9)
>   

Is there a white paper or other documentation around somewhere that
discusses the benefits/tradeoffs with using rmlock vs rwlock?

For example, how long can a write be delayed if there are lots of reads
being executed?  What sort of performance penalty does the write
suffer as a consequence of this vs rwlock, if any?

At what percentage of read vs write operations does it become better
to use rmlock vs rwlock?

Cheers,
Darren