netdev - Re: [patch iproute2 v6 0/3] tc: Add -bs option to batch mode

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Date:   Fri, 5 Jan 2018 18:25:23 +0100
From:   Phil Sutter <phil@....cc>
To:     Chris Mi <chrism@...lanox.com>
Cc:     netdev@...r.kernel.org, gerlitz.or@...il.com,
        stephen@...workplumber.org, dsahern@...il.com,
        marcelo.leitner@...il.com
Subject: Re: [patch iproute2 v6 0/3] tc: Add -bs option to batch mode

Hi Chris,

On Thu, Jan 04, 2018 at 04:34:51PM +0900, Chris Mi wrote:
> Currently in tc batch mode, only one command is read from the batch
> file and sent to kernel to process. With this patchset, we can accumulate
> several commands before sending to kernel. The batch size is specified
> using option -bs or -batchsize.
> 
> To accumulate the commands in tc, client should allocate an array of
> struct iovec. If batchsize is bigger than 1, only after the client
> has accumulated enough commands, can the client call rtnl_talk_msg
> to send the message that includes the iov array. One exception is
> that there is no more command in the batch file.
> 
> But please note that kernel still processes the requests one by one.
> To process the requests in parallel in kernel is another effort.
> The time we're saving in this patchset is the user mode and kernel mode
> context switch. So this patchset works on top of the current kernel.
> 
> Using the following script in kernel, we can generate 1,000,000 rules.
> 	tools/testing/selftests/tc-testing/tdc_batch.py
> 
> Without this patchset, 'tc -b $file' exection time is:
> 
> real    0m15.555s
> user    0m7.211s
> sys     0m8.284s
> 
> With this patchset, 'tc -b $file -bs 10' exection time is:
> 
> real    0m13.043s
> user    0m6.479s
> sys     0m6.504s
> 
> The insertion rate is improved more than 10%.

Did you measure the effect of increasing batch sizes?

I wonder whether specifying the batch size is necessary at all. Couldn't
batch mode just collect messages until either EOF or an incompatible
command is encountered which then triggers a commit to kernel? This
might simplify code quite a bit.

Cheers, Phil