LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Kai-Heng Feng <kai.heng.feng@canonical.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Heiner Kallweit <hkallweit1@gmail.com>,
	nic_swsd <nic_swsd@realtek.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Linux Netdev List <netdev@vger.kernel.org>,
	Linux PCI <linux-pci@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net-next v3 1/3] r8169: Implement dynamic ASPM mechanism
Date: Tue, 24 Aug 2021 15:39:35 +0800	[thread overview]
Message-ID: <CAAd53p5KH69NPMejM93STx3J+0WNBuXzaheWJJoURM39=DLvxg@mail.gmail.com> (raw)
In-Reply-To: <20210820210309.GA3357515@bjorn-Precision-5520>

On Sat, Aug 21, 2021 at 5:03 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Thu, Aug 19, 2021 at 05:45:22PM +0200, Heiner Kallweit wrote:
> > On 19.08.2021 13:42, Bjorn Helgaas wrote:
> > > On Thu, Aug 19, 2021 at 01:45:40PM +0800, Kai-Heng Feng wrote:
> > >> r8169 NICs on some platforms have abysmal speed when ASPM is enabled.
> > >> Same issue can be observed with older vendor drivers.
> > >
> > > On some platforms but not on others?  Maybe the PCIe topology is a
> > > factor?  Do you have bug reports with data, e.g., "lspci -vv" output?
> > >
> > >> The issue is however solved by the latest vendor driver. There's a new
> > >> mechanism, which disables r8169's internal ASPM when the NIC traffic has
> > >> more than 10 packets, and vice versa.
> > >
> > > Presumably there's a time interval related to the 10 packets?  For
> > > example, do you want to disable ASPM if 10 packets are received (or
> > > sent?) in a certain amount of time?
> > >
> > >> The possible reason for this is
> > >> likely because the buffer on the chip is too small for its ASPM exit
> > >> latency.
> > >
> > > Maybe this means the chip advertises incorrect exit latencies?  If so,
> > > maybe a quirk could override that?
> > >
> > >> Realtek confirmed that all their PCIe LAN NICs, r8106, r8168 and r8125
> > >> use dynamic ASPM under Windows. So implement the same mechanism here to
> > >> resolve the issue.
> > >
> > > What exactly is "dynamic ASPM"?
> > >
> > > I see Heiner's comment about this being intended only for a downstream
> > > kernel.  But why?
> > >
> > We've seen various more or less obvious symptoms caused by the broken
> > ASPM support on Realtek network chips. Unfortunately Realtek releases
> > neither datasheets nor errata information.
> > Last time we attempted to re-enable ASPM numerous problem reports came
> > in. These Realtek chips are used on basically every consumer mainboard.
> > The proposed workaround has potential side effects: In case of a
> > congestion in the chip it may take up to a second until ASPM gets
> > disabled, what may affect performance, especially in case of alternating
> > traffic patterns. Also we can't expect support from Realtek.
> > Having said that my decision was that it's too risky to re-enable ASPM
> > in mainline even with this workaround in place. Kai-Heng weights the
> > power saving higher and wants to take the risk in his downstream kernel.
> > If there are no problems downstream after few months, then this
> > workaround may make it to mainline.
>
> Since ASPM apparently works well on some platforms but not others, I'd
> suspect some incorrect exit latencies.

Can be, but if their dynamic ASPM mechanism can workaround the issue,
maybe their hardware is just designed that way?

>
> Ideally we'd have some launchpad/bugzilla links, and a better
> understanding of the problem, and maybe a quirk that makes this work
> on all platforms without mucking up the driver with ASPM tweaks.

The tweaks is OS-agnostic and is also implemented in Windows.

>
> But I'm a little out of turn here because the only direct impact to
> the PCI core is the pcie_aspm_supported() interface.  It *looks* like
> these patches don't actually touch the PCIe architected ASPM controls
> in Link Control; all I see is mucking with Realtek-specific registers.

AFAICT, Realtek ethernet NIC and wireless NIC both have two layers of
ASPM, one is the regular PCIe ASPM, and a Realtek specific internal
ASPM.
Both have to be enabled to really make ASPM work for them.

Kai-Heng

>
> I think this is more work than it should be and likely to be not as
> reliable as it should be.  But I guess that's up to you guys.
>
> Bjorn

  reply	other threads:[~2021-08-24  7:45 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-19  5:45 [PATCH net-next v3 0/3] r8169: Implement dynamic ASPM mechanism for recent 1.0/2.5Gbps Realtek NICs Kai-Heng Feng
2021-08-19  5:45 ` [PATCH net-next v3 1/3] r8169: Implement dynamic ASPM mechanism Kai-Heng Feng
2021-08-19 11:42   ` Bjorn Helgaas
2021-08-19 15:45     ` Heiner Kallweit
2021-08-20 21:03       ` Bjorn Helgaas
2021-08-24  7:39         ` Kai-Heng Feng [this message]
2021-08-24 14:53           ` Bjorn Helgaas
2021-08-27  4:56             ` Kai-Heng Feng
2021-08-19  5:45 ` [PATCH net-next v3 2/3] PCI/ASPM: Introduce a new helper to report ASPM support status Kai-Heng Feng
2021-08-19  5:45 ` [PATCH net-next v3 3/3] r8169: Enable ASPM for selected NICs Kai-Heng Feng
2021-08-19  6:02   ` Heiner Kallweit
2021-08-19  6:50     ` Kai-Heng Feng
2021-08-19  9:56       ` Heiner Kallweit
2021-08-27  6:23         ` Kai-Heng Feng
2021-08-19  6:08 ` [PATCH net-next v3 0/3] r8169: Implement dynamic ASPM mechanism for recent 1.0/2.5Gbps Realtek NICs Heiner Kallweit
2021-08-19  6:19   ` Kai-Heng Feng

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='CAAd53p5KH69NPMejM93STx3J+0WNBuXzaheWJJoURM39=DLvxg@mail.gmail.com' \
    --to=kai.heng.feng@canonical.com \
    --cc=bhelgaas@google.com \
    --cc=davem@davemloft.net \
    --cc=helgaas@kernel.org \
    --cc=hkallweit1@gmail.com \
    --cc=kuba@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=nic_swsd@realtek.com \
    --subject='Re: [PATCH net-next v3 1/3] r8169: Implement dynamic ASPM mechanism' \
    /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).