Subject: Re: TSO on wm(4) (Intel Pro/1000): i82546 vs i8254EI vs others?
To: Jonathan Stone <firstname.lastname@example.org>
From: Bill Studenmund <email@example.com>
Date: 05/24/2005 18:03:51
Content-Type: text/plain; charset=us-ascii
On Mon, May 23, 2005 at 08:32:29PM -0700, Jonathan Stone wrote:
> In message <20050524023918.GX5530@bcd.geek.com.au>,
> Daniel Carosone writes:
> >Agreed. There might be other reasons than performance you want to
> >toggle this (perhaps fault-finding: witness recent issues debugging
> >checksum over loopback vs offloading).
> >Perhaps the performance gain is better on slow cpu machines, or in MP
> >configs where biglock contention is an issue, or... etc.
> Hi Daniel,
> Have you seen Jason's message? Jason's report is that *intel* says TSO
> just doesn't work to spec on this chip; *Intel* issued an errata
> saying that TSO was no longer supported on the 82544 chip.
I think Jason's point is that it "works" but it doesn't work well. As=20
evidenced by the fact that groups still support it. It's not that it sends=
broken packets (in which case everyone'd want it turned off; see isses on=
the 82547 chip), it just doesn't do as well as one'd want/expect. It does=
better than "off", just only a little.
> The issue here is that a fairly expert admin (me) enabled the TSO
> capability on an 82544; but it didn't work, for a reasonable
> expectation of "work". Jason then explained that Intel issued an
> errata de-supporting TSO on the 82544.
So update the man page!
> I checked both the kernel source and (3.0 branch) manpages before
> posting. I didn't see any indication that there were known problems
> with TSO on 82544 chips. (Matt: I'm mildy curious, were you aware of
> that errata or not?)
Why are you asking if Matt has seen the errata? Jason wrote the driver...
> Anyway.... The minimum I'm asking for is that the driver print a
> shortattach-time (or enable-time) warning for i82544s chips: enough to
> alert an admin who *does* enable TSO on an i82544 to read an (updated)
> wm(4) manual page which explains this issue.
I don't think anyone will object to a driver message indicating that there=
is an issue with TSO on these chips.
> Daniel, Yamamoto-san: can one or other of you please explain to my why
> any that is a controversial thing to want? Because, sincerely, I'm not
> seeing _any_ reason why you, or Yamamoto-san, are opposed to it.
> I mean, do you expect Jason to explain the problem to everyone who
> does try to enable TSO on an 82544?
Are you really sure they are opposed to it? It sounded in your earlier=20
notes like you wanted to disable TSO on this chip entirely...
> In contrast, disabling the capability altogether on this chip version
> is far more heavy-handed: you'd have to build a custom kernel to
> re-enable the capability. That strikes me as a bit too heavy-handed...
and they were reacting to that. They felt (and it turns out agreed with=20
you) that turning the capability off was too drastic a move. Or at least=20
that's my take on it; I'll let them answer for what they thought.
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