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RE: [PATCH 2.6.12.1 5/12] S2io: Performance improvements

To: Raghavendra Koushik <raghavendra.koushik@xxxxxxxxxxxx>
Subject: RE: [PATCH 2.6.12.1 5/12] S2io: Performance improvements
From: Arthur Kepner <akepner@xxxxxxx>
Date: Fri, 8 Jul 2005 08:31:21 -0700 (PDT)
Cc: jgarzik@xxxxxxxxx, netdev@xxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, ravinandan.arakali@xxxxxxxxxxxx, leonid.grossman@xxxxxxxxxxxx, rapuru.sriram@xxxxxxxxxxxx
In-reply-to: <200507080106.j6816NKP022996@xxxxxxxxxxxxxxxxx>
References: <200507080106.j6816NKP022996@xxxxxxxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
On Thu, 7 Jul 2005, Raghavendra Koushik wrote:

> ....
> On an Altix machine I believe the readq was necessary to flush 
> the PIO writes. How long did you run the tests? I had seen
> in long duration tests that an occasional write 
> (TXDL control word and the address) would be missed and the xmit
> Get's stuck.
> 

The most recent tests I did used pktgen, and they ran for a total 
time of ~.5 hours (changing pkt_size every 30 seconds or so). The 
pktgen tests and other tests (like nttcp) have been run several times, 
so I've exercised the card for a total of several hours without 
any problems.

> 
> > 
> > FWIW, I've done quite a few performance measurements with the patch 
> > I posted earlier, and it's worked well. For 1500 byte mtus throughput 
> > goes up by ~20%. Is even the mmiowb() unnecessary?
> > 
> 
> Was this on 2.4 kernel because I think the readq would not have a 
> significant impact on 2.6 kernels due to TSO.
> (with TSO on the number of packets that actually enter the 
> Xmit routine would be reduced apprx 40 times).
> .....

This was with a 2.6 kernel (with TSO on). PIO reads are pretty 
expensive on Altix, so eliminating them really helps us. 

For big mtus (>=4KBytes) the benefit of replacing the readq()
with mmiowb() in s2io_xmit() is negligible. 

--
Arthur

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