linux-kernel - Re: [benchmark] 1% performance overhead of paravirt

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: <alpine.LFD.2.01.0906090924580.6847@localhost.localdomain>
Date:	Tue, 9 Jun 2009 09:26:47 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Rusty Russell <rusty@...tcorp.com.au>, Ingo Molnar <mingo@...e.hu>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Avi Kivity <avi@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native
 kernels



On Tue, 9 Jun 2009, Nick Piggin wrote:
> 
> The idea seems nice but isn't the problem that kmap gives back a
> basically 1st class kernel virtual memory? (ie. it can then be used
> by any other CPU at any point without it having to use kmap?).

No, everybody has to use kmap()/kunmap().

The "problem" is that you could in theory run out of kmap frames, since if 
everybody does a kmap() in an interruptible context and you have lots and 
lots of threads doing different pages, you'd run out. But that has nothing 
to do with kmap_atomic(), which is basically limited to just the number of 
CPU's and a (very small) level of nesting.

			Linus
--
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/