linux-kernel - Re: [4.2, Regression] Queued spinlocks cause major XFS performance regression

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: <20150908063725.GA2164@linux-q0g1.site>
Date:	Mon, 7 Sep 2015 23:37:25 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Waiman Long <Waiman.Long@...com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [4.2, Regression] Queued spinlocks cause major XFS performance
 regression

On Mon, 07 Sep 2015, Linus Torvalds wrote:

>On Sun, Sep 6, 2015 at 11:57 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> Just to continue the argument for arguments sake, the function is named
>> 'virt' (not paravirt) and tests the HYPERVISOR CPUID bit. How is that
>> not appropriately named?
>
>Well, I think right now one issue is that you can't avoid it, even
>when you want pure "raw hardware" spinlocks.
>
>I really think it should at the very least be inside CONFIG_PARAVIRT.

Yeah, I think we all agree here.

>Because it *is* about helping the hypervisor, so really is about
>paravirtualization.

Yes, this is how I interpret it as well.

CONFIG_PARAVIRT seems like a suitable place as while it is known to induce
in overhead for baremetal and distros tend to enable it by default - mainly
for mem pvops (ie: in page fault paths), and having this function doesn't
add any complexity or add make things much different than they already are.

While it is true that CONFIG_HYPERVISOR_GUEST is a pre-req for anything pv,
technically I think it's not as good a fit as CONFIG_PARAVIRT because the
former is really about describing the hypervisor, and that's not what we're
doing here.

Thanks,
Davidlohr
--
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/