On Sun, Oct 16, 2005 at 07:34:24PM -0700, Linus Torvalds wrote:
> On Sun, 16 Oct 2005, Dipankar Sarma wrote:
> >
> > Linus, I don't think this has anything to do with RCU grace periods
> > like we discussed previously. I measured on my 3.6GHz x86_64 and
> > found that open()/close() pair on /dev/null takes about 45500
> > cycles or 12 microseconds. [Does that sound resonable?].
>
> That sounds very slow. I can do a million open/close pairs in 4 seconds on
> a 2.5GHz G5. Maybe you tested a cold-cache case?
I measured after warming up for about a 100 times or so. It is
not a cold-cache case. I think we have a bigger problem in hand
here. I measured this with 2.6.13 and saw that I could do the
same in ~3 microseconds per iteration. It balloons to 12 microseconds
in 2.6.14-rc1. I am looking at this right now apart from the other
problems.
> I suspect this patch is worth it for the 2.6.14 timeframe, but I'll wait
> for confirmation.
>
> In fact, for 2.6.14, I'd almost do an even more minimal one. I agree with
> your changing the file counter to an atomic, but I'd rather keep that
> change for later.
Even beyond the file counter issue, we do need to address the DoS
and the open/close slowdown issue.
Thanks
Dipankar
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