linux-kernel - Re: [POC][RFC][PATCH] sched: Extended Scheduler Time Slice

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: <8734xyf00b.fsf@oracle.com>
Date:   Wed, 25 Oct 2023 22:03:48 -0700
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, willy@...radead.org, mgorman@...e.de,
        jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com,
        Joel Fernandes <joel@...lfernandes.org>,
        Youssef Esmat <youssefesmat@...omium.org>,
        Vineeth Pillai <vineethrp@...gle.com>,
        Suleiman Souhlal <suleiman@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...nel.org>
Subject: Re: [POC][RFC][PATCH] sched: Extended Scheduler Time Slice


Peter Zijlstra <peterz@...radead.org> writes:

> On Wed, Oct 25, 2023 at 05:42:19AM -0400, Steven Rostedt wrote:
>
>> So, bit 1 is for user space to tell the kernel "please extend me", and bit
>> two is for the kernel to tell user space "OK, I extended you, but call
>> sched_yield() when done".
>
> So what if it doesn't ? Can we kill it for not playing nice ?
>
> [ aside from it being bit 0 and bit 1 as you yourself point out, it is
>   also jarring you use a numeral for one and write out the other. ]
>
> That said, I properly hate all these things, extending a slice doesn't
> reliably work and we're always left with people demanding an ever longer
> extension.
>
> The *much* better heuristic is what the kernel uses, don't spin if the
> lock holder isn't running.

Something like vcpu_is_preempted()? That helps deal with preemption
once it has happened, but an ahead of time signal would be much more
efficient.

And, guest lock holder preemption was a big enough issue that we drop
down to test-and-set spinlocks in some cases.


Thanks

--
ankur