From: Alex G <mr.nuke.me@gmail.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: bhelgaas@google.com, helgaas@kernel.org,
linux-pci@vger.kernel.org, austin_bolen@dell.com,
alex_gagniuc@dellteam.com, keith.busch@intel.com,
Shyam_Iyer@Dell.com, lukas@wunner.de, okaya@kernel.org,
torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI/LINK: Account for BW notification in vector calculation
Date: Tue, 23 Apr 2019 11:03:04 -0500 [thread overview]
Message-ID: <88bd2962-bce4-8259-c38f-1a7e9fdde300@gmail.com> (raw)
In-Reply-To: <20190423093408.16b07efc@x1.home>
On 4/23/19 10:34 AM, Alex Williamson wrote:
> On Tue, 23 Apr 2019 09:33:53 -0500
> Alex G <mr.nuke.me@gmail.com> wrote:
>
>> On 4/22/19 7:33 PM, Alex Williamson wrote:
>>> On Mon, 22 Apr 2019 19:05:57 -0500
>>> Alex G <mr.nuke.me@gmail.com> wrote:
>>>> echo 0000:07:00.0:pcie010 |
>>>> sudo tee /sys/bus/pci_express/drivers/pcie_bw_notification/unbind
>>>
>>> That's a bad solution for users, this is meaningless tracking of a
>>> device whose driver is actively managing the link bandwidth for power
>>> purposes.
>>
>> 0.5W savings on a 100+W GPU? I agree it's meaningless.
>
> Evidence? Regardless, I don't have control of the driver that's making
> these changes, but the claim seems unfounded and irrelevant.
The number of 5mW/Gb/lane doesn't ring a bell? [1] [2]. Your GPU
supports 5Gb/s, so likely using an older, more power hungry process. I
suspect it's still within the same order of magnitude.
> I'm assigning a device to a VM [snip]
> I can see why we might want to be notified of degraded links due to signal issues,
> but what I'm reporting is that there are also entirely normal reasons
> [snip] we can't seem to tell the difference
Unfortunately, there is no way in PCI-Express to distinguish between an
expected link bandwidth change and one due to error.
If you're using virt-manager to configure the VM, then virt-manager
could have a checkbox to disable link bandwidth management messages. I'd
rather we avoid kernel-side heuristics (like Lukas suggested). If you're
confident that your link will operate as intended, and don't want
messages about it, that's your call as a user -- we shouldn't decide
this in the kernel.
Alex
[1]
https://www.synopsys.com/designware-ip/technical-bulletin/reduce-power-consumption.html
next prev parent reply other threads:[~2019-04-23 16:03 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-22 22:43 Alex Williamson
2019-04-23 0:05 ` Alex G
2019-04-23 0:33 ` Alex Williamson
2019-04-23 14:33 ` Alex G
2019-04-23 15:34 ` Alex Williamson
2019-04-23 15:49 ` Lukas Wunner
2019-04-23 16:03 ` Alex G [this message]
2019-04-23 16:22 ` Alex Williamson
2019-04-23 16:27 ` Alex G
2019-04-23 16:37 ` Alex Williamson
2019-04-23 17:10 ` Bjorn Helgaas
2019-04-23 17:53 ` Alex G
2019-04-23 18:38 ` Alex Williamson
2019-04-23 17:59 ` Alex G
2019-05-01 20:30 ` Bjorn Helgaas
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