Messages in this thread | | | Date | Wed, 17 Feb 2010 15:29:20 -0500 | From | David Teigland <> | Subject | Re: dlm: Remove/bypass astd |
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On Wed, Feb 17, 2010 at 01:23:39PM +0000, Steven Whitehouse wrote: > > While investigating Red Hat bug #537010 I started looking at the dlm's astd > thread. The way in which the "cast" and "bast" requests are queued looked > as if it might cause reordering since the "bast" requests are always > delivered after any pending "cast" requests which is not always the > correct ordering. This patch doesn't fix that bug, but it will prevent any > races in that bit of code, and the performance benefits are also well > worth having. > > I noticed that astd seems to be extraneous to requirements. The notifications > to astd are already running in process context, so they could be delivered > directly. That should improve smp performance since all the notifications > would no longer be funneled through a single thread. > > Also, the only other function of astd seemed to be stopping the delivery > of these notifications during recovery. Since, however, the notifications > which are intercepted at recovery time are neither modified, nor filtered > in any way, the only effect is to delay notifications for no obvious reason. > > I thought that probably removing the astd thread and delivering the "cast" > and "bast" notifications directly would improve performance due to the > elimination of a scheduling delay. I wrote a small test module which > creates a dlm lock space, and does 100,000 NL -> EX -> NL lock conversions. > > Having run this test 10 times each on a 2.6.33-rc8 kernel and then the modified > kernel including this patch, I got the following results: > > Original: Avg time 24.62 us per conversion (NL -> EX -> NL) > Modified: Avg time 9.93 us per conversion > > Which is a fairly dramatic speed up. Please consider applying this patch. > I've tested it in both clustered and single node GFS2 configurations. The test > figures are from a single node configuration which was a deliberate choice > in order to avoid any effects of network latency.
Wow, there's no chance I'm going to even consider something like this. This would be a huge change in how the dlm has always operated, and would surely introduce very serious and hard to identify bugs (and ones that may not appear for a long time afterward). Given that there's *no problem* with the current method that has worked well for years, any change would be completely crazy.
Dave
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