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Date: Fri, 30 Nov 2007 21:52:40 -0500 From: Mark Lord <lkml@....ca> To: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, abelay@...ell.com, lenb@...nel.org, mlord@...ox.com, rjw@...k.pl, linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org Subject: Re: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree Pallipadi, Venkatesh wrote: > > >> On Fri, 30 Nov 2007 14:06:55 -0800 >> "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> wrote: >> >> Please dont go off-list like this. I put Mark's original >> mailing list cc's >> back. > > Sorry for missing some cc's earlier. I blindly did a reply-all to the > mm-commits mail I got. > >>> I will have to Nack this. The reason max_cstate was initentionally >>> removed due to couple of reasons: >> It broke userspace without any warning or migration period, afaict. > > Yes. That's true. I will have to take the blame for that. It has been > known for a while during cpuidle development. But, it was never > documented as deprecating. > >>> 1) All in kernel users of max_cstate should rather be using >>> pm_qos/latency interfaces. All such max_cstate usages must already be >>> migrated. >> That code isn't merged. > > All kernel part is already merged. I mean, there are do drivers that > depend on max_cstate. They use latency_notifier thing today and their > migration to pm_qos part is not merged yet. > >>> 2) Supporting max_cstate as a dynamic parameter cleanly is no longer >>> possible in acpi/processor_idle.c as the C-state policy has moved to >>> cpuidle instead. It can be done if it is needed. But, just >> below patch >>> will not really work with cpuidle. >>> >>> Selecting max_cstate at boot time as a debug option still >> works without >>> this patch. >>> >>> So, just this patch will not get back the functionality with cpuidle. >>> Infact changing it at run time will have no effect. Question >> however is: >>> Is there a real need to revive this parameter so that user can change >>> max_cstate at run time? >> It is not known whether Mark is actually writing to this >> thing. Perhaps >> read-only permissions would be a suitable fix? >> > > Exporting it as read only should be OK. We also need to know if there > are hard user space dependency on writing to this from userspace. .. Well, actually.. my scripts have a firm need to write "1" to it, and then later restore the original value. This is needed to *greatly* speed up an otherwise sluggish binary I use, as well as whenever I want to semi-accurately benchmark I/O. Is there another way to achieve exactly the same behaviour? Thanks - 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/
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