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Date: Tue, 01 Mar 2022 15:14:58 -0500 From: Olivier Langlois <olivier@...llion01.com> To: Hao Xu <haoxu@...ux.alibaba.com>, Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com> Cc: io-uring <io-uring@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v4 2/2] io_uring: Add support for napi_busy_poll On Tue, 2022-03-01 at 15:06 -0500, Olivier Langlois wrote: > On Wed, 2022-03-02 at 02:31 +0800, Hao Xu wrote: > > > > > > How about: > > > > if (list is singular) { > > > > do something; > > > > return; > > > > } > > > > while (!io_busy_loop_end() && io_napi_busy_loop()) > > > > ; > > > > is there a concern with the current code? > What would be the benefit of your suggestion over current code? > > To me, it seems that if io_blocking_napi_busy_loop() is called, a > reasonable expectation would be that some busy looping is done or > else > you could return the function without doing anything which would, > IMHO, > be misleading. > > By definition, napi_busy_loop() is not blocking and if you desire the > device to be in busy poll mode, you need to do it once in a while or > else, after a certain time, the device will return back to its > interrupt mode. > > IOW, io_blocking_napi_busy_loop() follows the same logic used by > napi_busy_loop() that does not call loop_end() before having perform > 1 > loop iteration. > > > Btw, start_time seems not used in singular branch. > > I know. This is why it is conditionally initialized. > > Greetings, > Another argument for not touching the code the way that it is: io_napi_busy_loop() has another function on top of iterating the napi_list and calling napi_busy_loop() for each of them. The function also check the list entries validity and frees them when they time out. Not calling io_napi_busy_loop() you would bypass this check and that could result in timed out entries to never be disposed.
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