netdev - Re: [patch 1/4] - Potential performance bottleneck for Linxu TCP

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: <20061130065627.GE2003@elte.hu>
Date:	Thu, 30 Nov 2006 07:56:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	wenji@...l.gov, akpm@...l.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] - Potential performance bottleneck for Linxu TCP

* David Miller <davem@...emloft.net> wrote:

> This is why my suggestion is to preempt_disable() as soon as we grab 
> the socket lock, [...]

independently of the issue at hand, in general the explicit use of 
preempt_disable() in non-infrastructure code is quite a heavy tool. Its 
effects are heavy and global: it disables /all/ preemption (even on 
PREEMPT_RT). Furthermore, when preempt_disable() is used for per-CPU 
data structures then [unlike for example to a spin-lock] the connection 
between the 'data' and the 'lock' is not explicit - causing all kinds of 
grief when trying to convert such code to a different preemption model. 
(such as PREEMPT_RT :-)

So my plan is to remove all "open-coded" use of preempt_disable() [and 
raw use of local_irq_save/restore] from the kernel and replace it with 
some facility that connects data and lock. (Note that this will not 
result in any actual changes on the instruction level because internally 
every such facility still maps to preempt_disable() on non-PREEMPT_RT 
kernels, so on non-PREEMPT_RT kernels such code will still be the same 
as before.)

	Ingo
-
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