linux-kernel - Re: The purpose and implementation of cond

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] [day] [month] [year] [list]

Message-ID: <a2ebde260702210908o52b93002u19e8200b6b56ae5a@mail.gmail.com>
Date:	Thu, 22 Feb 2007 01:08:25 +0800
From:	"Dong Feng" <middle.fengdong@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: The purpose and implementation of cond_resched()

I re-checked the code. And this time, I think cond_resched() is useful
while a kernel is compiled with no full preemption function but only
voluntary kernel preemption is enabled (i.e. CONFIG_PREEMPT_VOLUNTARY
is set but CONFIG_PREEMPT is not set). In this case, kernel performs
scheduling at explicit voluntary preemption points only, and those
points are determined by invoking cond_resched().

But I still have questions, why cond_resched() does not yield no-op
while CONFIG_PREEMPT is set? And why does it deal with the
PREEMPT_ACTIVE flag anyway?



2007/2/22, Dong Feng <middle.fengdong@...il.com>:
> I have a question about cond_resched().
>
> What is the condition under which I should invoke cond_resched() irreplaceably?
>
> For example, I see the following code in ksoftirqd(),
>
> preempt_enable_no_resched();
> cond_resched();
> preempt_disable();
>
> But I do not understand why I should not write the following code,
>
> preempt_enable();
> preempt_disable();
>
> Are the above two pieces of code equal in functionality?
>
> On the other hand, I see cond_resched() check and set PREEMPT_ACTIVE.
> I currently do not understand why it should do this, since I think
> PREEMPT_ACTIVE is only used to be set in the return-from-interrupt
> code in order to prevent schedule() from removing task from run queue
> unpredictably. But for cond_resched(), which is a planned voluntary
> switch, why does it also deal with this flag?
>
-
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/