On Sun, 1 Apr 2007, Robert Watson wrote:
The attached patch moves file descriptor locks from being a custom
mutex/sleep lock implemented using msleep() to an sx lock. With the new sx
lock optimizations in place, this is now sensible, avoiding both a custom
lock type and significantly improving performance. Kris has reported 2x-4x
improvement in transactions/sec with MySQL using this patch, as it greatly
reduces the cost of lock contention during file descriptor lookup for
threaded applications, and also moves to shared locking to avoid exclusive
acquisition for read-only operations (the vast majority in most workloads).
Patch is below, but you can also download from:
http://www.watson.org/~robert/freebsd/netperf/20070401a-filedesc-sx.diff
I'm currently waiting for the sx lock changes to settle for a few days
before committing, so will plan to commit this around Wednesday/Thursday of
this week (unless serious problems arise).
Andrzej has pointed out that shortly after I posted the patch, it came into
conflict with changes in VFS. I've updated the patch and posted it at:
http://www.watson.org/~robert/freebsd/netperf/20070403-filedesc-sx.diff
Thanks,
Robert N M Watson
Computer Laboratory
University of Cambridge
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