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Date: Sun, 1 Mar 2020 01:02:39 -0800 From: Josh Triplett <josh@...htriplett.org> To: Chaitanya Kulkarni <Chaitanya.Kulkarni@....com> Cc: Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org> Subject: Re: [PATCH] nvme: Check for readiness more quickly, to speed up boot time On Sun, Mar 01, 2020 at 02:01:05AM +0000, Chaitanya Kulkarni wrote: > Nit:- please have a look at the patch subject line and make > sure it is not exceeding the required length. Documentation/process/submitting-patches.rst says "no more than 70-75 characters,", and the summary here is 61. Checkpatch similarly says 75. Is there somewhere I missed that gives a different number? > One question though, have you seen similar kind of performance > improvements when system is booted ? I tested with nvme compiled in, both with one NVMe device and two NVMe devices, and in both cases it provided a *substantial* speedup. I didn't test nvme compiled as a module, but in general I'd expect that if you're trying to optimize initialization time you'd want to build it in. > I took some numbers and couldn't see similar benefit. See [1] :- > > Without :- > > 714.532560-714.456099 = .076461 > 721.189886-721.110845 = .079041 > 727.836938-727.765572 = .071366 > 734.589886-734.519779 = .070107 > 741.244296-741.173503 = .070793 With numbers in this range, I don't see how you could be hitting the 100ms msleep at all, even once, which means this patch shouldn't have any effect on the timing you're measuring. - Josh Triplett
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