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Date: Thu, 4 Apr 2013 01:45:36 +0400
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: Brooks Davis <brooks@FreeBSD.org>
Subject: Re: [CFR][CFT] counter(9): new API for faster and raceless counters
Message-ID: <20130403214536.GJ76816@glebius.int.ru>
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 <20130403190533.GA97453@lor.one-eyed-alien.net>
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On Wed, Apr 03, 2013 at 02:05:33PM -0500, Brooks Davis wrote:
B> > o Tiny API for counter(9):
B> > 
B> >      counter_u64_t
B> >      counter_u64_alloc(int wait);
B> > 
B> >      void
B> >      counter_u64_free(counter_u64_t cnt);
B> > 
B> >      void
B> >      counter_u64_add(counter_u64_t cnt, uint64_t inc);
B> > 
B> >      uint64_t
B> >      counter_u64_fetch(counter_u64_t cnt);
B> 
B> I wonder if there might be value in an interface to retrieve the per-cpu
B> values individually.  The use case I have in mind is interrupt counters
B> on our BERI CPU.  Similar to the Sibyte MIPS SoCs, our PIC always routes
B> each interrupt to a specific hardware thread.  I'd ideally like to be able
B> to look at at hardware interrupts on a per-thread basis and avoid the
B> cache trashing behavior we'd get if we allocated current interrupt
B> counters to each one, but we probably want to be able to preserve
B> something like the current behavior.

You can just utilize directly the per-CPU UMA zones, that will come together
with counter(9).

So, the code will look like:

critical_enter();

foo = (foo *)zpcpu_get(base);	/* get private to CPU data */

do smth with foo

critical_exit();


-- 
Totus tuus, Glebius.