linux-kernel - Re: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags

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: <eeb80957-96f7-661c-1510-0e6247570bd3@redhat.com>
Date:   Sun, 16 Aug 2020 14:16:07 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in
 pageblock flags

On 16.08.20 05:47, Alex Shi wrote:
> pageblock_flags is used as long, since every pageblock_flags is just 4
> bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flags,
> that flag setting has to sync in cmpxchg with 7 or 15 other pageblock
> flags. It would cause long waiting for sync.
> 
> If we could change the pageblock_flags variable as char, we could use
> char size cmpxchg, which just sync up with 2 pageblock flags. it could
> relief much false sharing in cmpxchg.

Do you have any performance numbers to back your claims? IOW, do we care
at all?



-- 
Thanks,

David / dhildenb