From: Andrew Morton <akpm@osdl.org>
To: Eric Dumazet <dada1@cosmosbay.com>
Cc: kiran@scalex86.org, davem@davemloft.net,
linux-kernel@vger.kernel.org, shai@scalex86.org,
netdev@vger.kernel.org, pravins@calsoftinc.com
Subject: Re: [patch 3/4] net: Percpufy frequently used variables -- proto.sockets_allocated
Date: Fri, 27 Jan 2006 15:16:35 -0800 [thread overview]
Message-ID: <20060127151635.3a149fe2.akpm@osdl.org> (raw)
In-Reply-To: <43DAA586.5050609@cosmosbay.com>
Eric Dumazet <dada1@cosmosbay.com> wrote:
>
> Ravikiran G Thirumalai a écrit :
> > On Fri, Jan 27, 2006 at 12:16:02PM -0800, Andrew Morton wrote:
> >> Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> >>> which can be assumed as not frequent.
> >>> At sk_stream_mem_schedule(), read_sockets_allocated() is invoked only
> >>> certain conditions, under memory pressure -- on a large CPU count machine,
> >>> you'd have large memory, and I don't think read_sockets_allocated would get
> >>> called often. It did not atleast on our 8cpu/16G box. So this should be OK
> >>> I think.
> >> That being said, the percpu_counters aren't a terribly successful concept
> >> and probably do need a revisit due to the high inaccuracy at high CPU
> >> counts. It might be better to do some generic version of vm_acct_memory()
> >> instead.
> >
> > AFAICS vm_acct_memory is no better. The deviation on large cpu counts is the
> > same as percpu_counters -- (NR_CPUS * NR_CPUS * 2) ...
>
> Ah... yes you are right, I read min(16, NR_CPUS*2)
So did I ;)
> I wonder if it is not a typo... I mean, I understand the more cpus you have,
> the less updates on central atomic_t is desirable, but a quadratic offset
> seems too much...
I'm not sure whether it was a mistake or if I intended it and didn't do the
sums on accuracy :(
An advantage of retaining a spinlock in percpu_counter is that if accuracy
is needed at a low rate (say, /proc reading) we can take the lock and then
go spill each CPU's local count into the main one. It would need to be a
very low rate though. Or we make the cpu-local counters atomic too.
Certainly it's sensible to delegate the tuning to the creator of the
percpu_counter, but it'll be a difficult thing to get right.
next prev parent reply other threads:[~2006-01-27 23:14 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-26 18:56 [patch 0/4] net: Percpufy frequently used variables on struct proto Ravikiran G Thirumalai
2006-01-26 18:59 ` [patch 1/4] net: Percpufy frequently used variables -- add percpu_counter_mod_bh Ravikiran G Thirumalai
2006-01-26 19:02 ` [patch 2/4] net: Percpufy frequently used variables -- struct proto.memory_allocated Ravikiran G Thirumalai
2006-01-27 9:01 ` Eric Dumazet
2006-01-26 19:03 ` [patch 3/4] net: Percpufy frequently used variables -- proto.sockets_allocated Ravikiran G Thirumalai
2006-01-27 8:53 ` Eric Dumazet
2006-01-27 19:52 ` Ravikiran G Thirumalai
2006-01-27 20:16 ` Andrew Morton
2006-01-27 22:30 ` Eric Dumazet
2006-01-27 22:50 ` Ravikiran G Thirumalai
2006-01-27 23:21 ` Eric Dumazet
2006-01-28 0:40 ` Ravikiran G Thirumalai
2006-01-27 22:44 ` Ravikiran G Thirumalai
2006-01-27 22:58 ` Eric Dumazet
2006-01-27 23:16 ` Andrew Morton [this message]
2006-01-28 0:28 ` Eric Dumazet
2006-01-28 0:35 ` Eric Dumazet
2006-01-28 4:52 ` Ravikiran G Thirumalai
2006-01-28 7:19 ` Eric Dumazet
2006-01-28 0:43 ` Andrew Morton
2006-01-28 1:10 ` Eric Dumazet
2006-01-28 1:18 ` Andrew Morton
2006-01-29 0:44 ` Benjamin LaHaise
2006-01-29 0:55 ` Andrew Morton
2006-01-29 1:19 ` Benjamin LaHaise
2006-01-29 1:29 ` Andrew Morton
2006-01-29 1:45 ` Kyle McMartin
2006-01-29 5:38 ` Andi Kleen
2006-01-29 6:54 ` Eric Dumazet
2006-01-29 19:52 ` Benjamin LaHaise
2006-01-27 23:01 ` Andrew Morton
2006-01-27 23:08 ` Andrew Morton
2006-01-28 0:01 ` Ravikiran G Thirumalai
2006-01-28 0:26 ` Andrew Morton
2006-02-03 3:05 ` Ravikiran G Thirumalai
2006-02-03 3:16 ` Andrew Morton
2006-02-03 19:37 ` Ravikiran G Thirumalai
2006-02-03 20:13 ` Andrew Morton
2006-01-26 19:05 ` [patch 4/4] net: Percpufy frequently used variables -- proto.inuse Ravikiran G Thirumalai
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