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Date: Wed, 29 Oct 2014 12:57:00 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Jeff Kirsher <jeffrey.t.kirsher@...el.com> Cc: Alexander Duyck <alexander.h.duyck@...hat.com>, netdev <netdev@...r.kernel.org> Subject: Re: [RFC] use smp_load_acquire()/smp_store_release() On Wed, 2014-10-29 at 12:27 -0700, Jeff Kirsher wrote: > On Wed, 2014-10-29 at 09:16 -0700, Alexander Duyck wrote: > > On 10/29/2014 07:49 AM, Eric Dumazet wrote: > > > Hi Alexander > > > > > > The memory barriers added in commit > > > b37c0fbe3f6dfba1f8ad2aed47fb40578a254635 > > > ("net: Add memory barriers to prevent possible race in byte queue > > > limits") > > > > > > have heavy cost. > > > > > > It seems we could use smp_load_acquire() and smp_store_release() > > > instead ? > > > > > > I'll post a patch later today. I would be interested if someone was able > > > to test it, as your commit apparently was tested and known to fix a > > > reproducible race. > > > > > > Thanks ! > > Eric- just CC me on the patch you post and I will see what I can do > about getting validation eyes on it. Thanks guys, will do, and will CC Paul as well. Alexander, here is the following profile showing the cost of the 'mfence', in a typical rpc workload (a lot of IRQ are generated for TX completions, because RPC tend to send small packets) 0.11 │ je 33a │ mov -0x3c(%rbp),%esi 0.06 │ lea 0xc0(%rbx),%rdi 0.06 │ callq dql_completed 0.06 │ mfence 38.68 │ mov 0xc4(%rbx),%edx 1.83 │ mov 0xc0(%rbx),%eax │ cmp %eax,%edx 0.22 │ js 333 0.11 │ lock btrl $0x1,0x98(%rbx) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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