linux-pci.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=88bd2962-bce4-8259-c38f-1a7e9fdde300@gmail.com \
    --to=mr.nuke.me@gmail.com \
    --cc=Shyam_Iyer@Dell.com \
    --cc=alex.williamson@redhat.com \
    --cc=alex_gagniuc@dellteam.com \
    --cc=austin_bolen@dell.com \
    --cc=bhelgaas@google.com \
    --cc=helgaas@kernel.org \
    --cc=keith.busch@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=lukas@wunner.de \
    --cc=okaya@kernel.org \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [PATCH] PCI/LINK: Account for BW notification in vector calculation' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).