Re: [PATCH V2 0/2] enable irqs when waiting for rwlocks

Robin Holt
2008-11-03T11:46:39Z

On Fri, Oct 31, 2008 at 01:22:56PM -0700, Luck, Tony wrote:
> > Any comments on my second patch series? Not even an Acked-by? Dislike of
> > the concept? Should I post it again?
>
> Better response to interrupts is good, but it comes at the
> cost of longer latency acquiring the lock (in the case where
> an interrupt happens while we are waiting for the lock, and
> the lock is freed while we are off executing the interrupt
> handler).
>
> Any suggestions on how to measure the trade-off here? Possibly
> it doesn't matter because this may only be significant when
> the lock is heavily contended and you are probably aleady
> hosed in this case.

Just a few years of experiencal evidence. The equivalent of this patch
has been in the SuSE SLES10 kernel for years and not been detected as
being negative.

Sorry I don't have more detail. The person at SGI who first detected
this problem has long since left, and actually passed away from an
aneurysm a couple years ago. The first version of the patch was in our
one-off kernel based on Redhat's 2.4 kernel. The patch was not pushed
to SuSE and the community for SLES9. It was in SLES10, but I can not
find our internal tracking tool's record of it (searching is failing me
this morning). Without that, I have not been able to find why it was
not pushed to the community.

Thanks,
Robin