From: Paolo Bonzini <pbonzini@redhat.com>
To: Xiao Guangrong <guangrong.xiao@linux.intel.com>,
Lan Tianyu <tianyu.lan@intel.com>,
Thomas Gleixner <tglx@linutronix.de>
Cc: gleb@kernel.org, mingo@redhat.com, hpa@zytor.com, x86@kernel.org,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: Remove redundant smp_mb() in the kvm_mmu_commit_zap_page()
Date: Thu, 10 Mar 2016 17:04:49 +0100 [thread overview]
Message-ID: <56E19B21.8090501@redhat.com> (raw)
In-Reply-To: <56E196AC.4030103@linux.intel.com>
On 10/03/2016 16:45, Xiao Guangrong wrote:
>>
>>> Compared to smp_load_acquire(), smp_mb() adds an ordering between stores
>>> and loads.
>>
>> Here, the ordering is load-store, hence...
>
> Yes, this is why i put smp_mb() in the code. :)
Here is a table of barriers:
'. after| |
before '. | load | store
__________'.|___________________|________________________
| |
| smp_rmb | smp_load_acquire
load | smp_load_acquire | smp_store_release XX
| smp_mb | smp_mb
____________|___________________|________________________
| |
| | smp_wmb
store | smp_mb | smp_store_release
| | smp_mb
| |
Your case is the one marked with XX, so a smp_load_acquire() is
enough---and it's preferrable, because it's cheaper than smp_mb() and
more self-documenting.
Paolo
next prev parent reply other threads:[~2016-03-10 16:04 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-04 1:35 [PATCH] KVM: Remove redundant smp_mb() in the kvm_mmu_commit_zap_page() Lan Tianyu
2016-03-04 7:21 ` Thomas Gleixner
2016-03-04 7:12 ` Lan Tianyu
2016-03-04 8:49 ` Paolo Bonzini
2016-03-08 8:36 ` Lan Tianyu
2016-03-08 15:27 ` Paolo Bonzini
2016-03-09 7:18 ` Lan Tianyu
2016-03-10 17:07 ` Paolo Bonzini
2016-03-10 18:08 ` Xiao Guangrong
2016-03-10 14:40 ` Xiao Guangrong
2016-03-10 15:26 ` Paolo Bonzini
2016-03-10 15:31 ` Paolo Bonzini
2016-03-10 15:45 ` Xiao Guangrong
2016-03-10 16:04 ` Paolo Bonzini [this message]
2016-03-10 17:57 ` Xiao Guangrong
2016-03-11 1:13 ` Lan Tianyu
2016-03-04 8:04 ` Paolo Bonzini
2016-03-04 13:48 ` Xiao Guangrong
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