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Re: 1.03Mpps on e1000 (was: Re: [E1000-devel] Transmission limit)

To: Scott Feldman <sfeldma@xxxxxxxxx>
Subject: Re: 1.03Mpps on e1000 (was: Re: [E1000-devel] Transmission limit)
From: Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx>
Date: Sun, 5 Dec 2004 22:25:59 +0100
Cc: Martin Josefsson <gandalf@xxxxxxxxxxxxxx>, jamal <hadi@xxxxxxxxxx>, Robert Olsson <Robert.Olsson@xxxxxxxxxxx>, P@xxxxxxxxxxxxxx, mellia@xxxxxxxxxxxxxxxxxxxx, e1000-devel@xxxxxxxxxxxxxxxxxxxxx, Jorge Manuel Finochietto <jorge.finochietto@xxxxxxxxx>, Giulio Galante <galante@xxxxxxxxx>, netdev@xxxxxxxxxxx
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On Sun, Dec 05, 2004 at 01:12:22PM -0800, Scott Feldman wrote:

> Would Martin or Lennert run these test for a longer duration so we can
> get some data, maybe adding in Rx.  It could be that removing the Tx
> interrupts and descriptor write-backs, prefetching may be ok.  I don't
> know.  Intel?

What your patch does is (correct me if I'm wrong):
- Masking TXDW, effectively preventing it from delivering TXdone ints.
- Not setting E1000_TXD_CMD_IDE in the TXD command field, which causes
  the chip to 'ignore the TIDV' register, which is the 'TX Interrupt
  Delay Value'.  What exactly does this?
- Not setting the "Report Packet Sent"/"Report Status" bits in the TXD
  command field.  Is this the equivalent of the TXdone interrupt?

Just exactly which bit avoids the descriptor writeback?

I'm also a bit worried that only freeing packets 1ms later will mess up
socket accounting and such.  Any ideas on that?

> Also, wouldn't it be great if someone wrote a document capturing all of
> the accumulated knowledge for future generations?

I'll volunteer for that.


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