From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Ming Lei <tom.leiming@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
mark gross <mgross@linux.intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM List <linux-pm@vger.kernel.org>
Subject: Re: [Question] PM-QoS: PM_QOS_CPU_DMA_LATENCY == interrupt latency?
Date: Mon, 10 Oct 2011 17:25:57 +0100 [thread overview]
Message-ID: <20111010172557.332bfe30@lxorguk.ukuu.org.uk> (raw)
In-Reply-To: <CACVXFVOkwX+974=eEY5UPysXN-t9Adg6=Wn0Ts4m0vT5zQaw3g@mail.gmail.com>
On Mon, 10 Oct 2011 22:31:34 +0800
Ming Lei <tom.leiming@gmail.com> wrote:
> Hi,
>
> Looks like it is a bit difficult to understand PM_QOS_CPU_DMA_LATENCY
> from the words' meaning.
>
> After searching from google, I don't find some useful information about
> the root cause for introducing PM_QOS_CPU_DMA_LATENCY. I understand
> it is very similar to interrupt latency. Also from the comment for
> omap_pm_set_max_mpu_wakeup_lat in file[1], the description is basically same
> with interrupt latency.
>
> >From comments of pm_qos_add_request usages in drivers, it can be understood
> as interrupt latency too, IMO.
>
> So, could we think that PM_QOS_CPU_DMA_LATENCY is interrupt latency?
No. Well it may be on some platforms but it isn't the same thing. On some
devices a DMA transfer doesn't need the CPU involved but needs the CPU to
respond within a set timescale (eg for coherency or bus arbitration). It
is not the same thing as IRQ latency.
next prev parent reply other threads:[~2011-10-10 16:27 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-10 14:31 Ming Lei
2011-10-10 16:25 ` Alan Cox [this message]
2011-10-11 1:28 ` Ming Lei
2011-10-11 1:49 ` Shaohua Li
2011-10-11 2:18 ` Ming Lei
2011-10-11 2:26 ` Shaohua Li
2011-10-11 3:40 ` Ming Lei
2011-10-11 5:32 ` Shaohua Li
2011-10-11 9:36 ` Ming Lei
2011-10-11 10:07 ` Alan Cox
2011-10-11 10:56 ` Ming Lei
2011-10-13 4:06 ` mark gross
2011-10-13 14:52 ` Ming Lei
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