Subject: Re: [PATCH net-next 2/2] sunvnet: Re-check for a VIO_DESC_READY data descriptor after short udelay()

From: Sowmini Varadhan <[email-masked]>
Date: Tue, 02 Sep 2014 06:27:54 -0400

On 09/01/2014 11:47 PM, David Miller wrote:

>
> If there were no more packets coming, this is wasted useless polling
> time in atomic context.

turns out that this gives a 20-30% perf improvement for tests like
iperf.

when there are no more packets coming, the extra 12 microsecond
delay is not that big of a deal anyway. The point was that the extra
12 micro-second tax in the quiescent network state is less expensive
than exiting interrupt context, taking another interrupt and doing
another ldc_read, when there is actually a burst of packets.

notice that there are many other such udelay() loops elsewhere in
the code.

I can remove the retries and submit patch 1/1 again later today.

>
> Everything should be event based, and we should not be compensating
> and making sacrifices for a producer slower than we are as a consumer.
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