linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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: <20070421165347.GA26903@elte.hu>
Date:	Sat, 21 Apr 2007 18:53:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Willy Tarreau <w@....eu>, Con Kolivas <kernel@...ivas.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> It would be even better to simply have the rule:
>  - child gets almost no points at startup
>  - but when a parent does a "waitpid()" call and blocks, it will spread 
>    out its points to the childred (the "vfork()" blocking is another case 
>    that is really the same).
> 
> This is a very special kind of "priority inversion" logic: you give 
> higher priority to the things you wait for. Not because of holding any 
> locks, but simply because a blockign waitpid really is a damn big hint 
> that "ok, the child now works for the parent".

yeah. One problem i can see with the implementation of this though is 
that shells typically do nonspecific waits - for example bash does this 
on a simple 'ls' command:

  21310 clone(child_stack=0,  ...) = 21399
  ...
  21399 execve("/bin/ls", 
  ...
  21310 waitpid(-1, <unfinished ...>

the PID is -1 so we dont actually know which task we are waiting for. We 
could use the first entry from the p->children list, but that looks too 
specific of a hack to me. It should catch most of the 
synchronous-helper-task cases though.

	Ingo
-
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/