linux-kernel - RE: [PATCH 2/2] intel_idle: Introduce 'states

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]

Date:   Fri, 31 Jan 2020 11:54:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'artem.bityutskiy@...ux.intel.com'" 
        <artem.bityutskiy@...ux.intel.com>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
CC:     Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>,
        Zhang Rui <rui.zhang@...el.com>,
        David Box <david.e.box@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: RE: [PATCH 2/2] intel_idle: Introduce 'states_off' module parameter

From: Artem Bityutskiy >
> Sent: 31 January 2020 11:24
> On Fri, 2020-01-31 at 11:07 +0000, David Laight wrote:
> > Unless you know exactly which cpu table is being used the
> > only constraint a user can request is the latency.
> 
> Hi David,
> 
> in all my use-cases I always know what is the CPU I am dealing with and
> what are the C-states. Simply because in my view they are always CPU-
> dependent in terms of what they do and how are they named.
> 
> What you say sounds to me like you would want to disable some C-states
> without knowing anything (or much) about the CPU you are dealing with
> and the C-state names.
> 
> If so, could you please share examples of such use-cases?

Dunno, but clearly you want to disable (say) C3 while leaving C6
enabled.

I was trying to find why it was taking 600+us for a RT process
to get rescheduled when it had only been sleeping for a few us.

I found where it was sleeping, but that didn't help at all.
Someone pointed me at a 'random' pdf that referred to /dev/cpu_dma_latency.
Setting that to a small value (eg 20) helps no end.
But there are no references in the code or man pages to that.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)