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Date:   Wed, 22 May 2019 18:00:58 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sunilmut@...rosoft.com
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        sashal@...nel.org, mikelley@...rosoft.com, netdev@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] hv_sock: perf: loop in send() to maximize
 bandwidth

From: Sunil Muthuswamy <sunilmut@...rosoft.com>
Date: Wed, 22 May 2019 23:10:44 +0000

> Currently, the hv_sock send() iterates once over the buffer, puts data into
> the VMBUS channel and returns. It doesn't maximize on the case when there
> is a simultaneous reader draining data from the channel. In such a case,
> the send() can maximize the bandwidth (and consequently minimize the cpu
> cycles) by iterating until the channel is found to be full.
> 
> Perf data:
> Total Data Transfer: 10GB/iteration
> Single threaded reader/writer, Linux hvsocket writer with Windows hvsocket
> reader
> Packet size: 64KB
> CPU sys time was captured using the 'time' command for the writer to send
> 10GB of data.
> 'Send Buffer Loop' is with the patch applied.
> The values below are over 10 iterations.
 ...
> Observation:
> 1. The avg throughput doesn't really change much with this change for this
> scenario. This is most probably because the bottleneck on throughput is
> somewhere else.
> 2. The average system (or kernel) cpu time goes down by 10%+ with this
> change, for the same amount of data transfer.
> 
> Signed-off-by: Sunil Muthuswamy <sunilmut@...rosoft.com>

Applied.

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