linux-kernel - Re: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4E0B09EA.1040304@redhat.com>
Date:	Wed, 29 Jun 2011 14:18:02 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table

On 06/29/2011 02:16 PM, Xiao Guangrong wrote:
> >>  @@ -1767,6 +1874,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
> >>
> >>        kvm_flush_remote_tlbs(kvm);
> >>
> >>  +    if (atomic_read(&kvm->arch.reader_counter)) {
> >>  +        kvm_mmu_isolate_pages(invalid_list);
> >>  +        sp = list_first_entry(invalid_list, struct kvm_mmu_page, link);
> >>  +        list_del_init(invalid_list);
> >>  +        call_rcu(&sp->rcu, free_pages_rcu);
> >>  +        return;
> >>  +    }
> >>  +
> >
> >  I think we should do this unconditionally.  The cost of ping-ponging the shared cache line containing reader_counter will increase with large smp counts.  On the other hand, zap_page is very rare, so it can be a little slower.  Also, less code paths = easier to understand.
> >
>
> On soft mmu, zap_page is very frequently, it can cause performance regression in my test.

Any idea what the cause of the regression is?  It seems to me that 
simply deferring freeing shouldn't have a large impact.

-- 
error compiling committee.c: too many arguments to function

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/