On 3/24/23 10:46 PM, Al Viro wrote: > On Fri, Mar 24, 2023 at 02:44:41PM -0600, Jens Axboe wrote: >> Hi, >> >> We've been doing a few conversions of ITER_IOVEC to ITER_UBUF in select >> spots, as the latter is cheaper to iterate and hence saves some cycles. >> I recently experimented [1] with io_uring converting single segment READV >> and WRITEV into non-vectored variants, as we can save some cycles through >> that as well. >> >> But there's really no reason why we can't just do this further down, >> enabling it for everyone. It's quite common to use vectored reads or >> writes even with a single segment, unfortunately, even for cases where >> there's no specific reason to do so. From a bit of non-scientific >> testing on a vm on my laptop, I see about 60% of the import_iovec() >> calls being for a single segment. >> >> I initially was worried that we'd have callers assuming an ITER_IOVEC >> iter after a call import_iovec() or import_single_range(), but an audit >> of the kernel code actually looks sane in that regard. Of the ones that >> do call it, I ran the ltp test cases and they all still pass. > > Which tree was that audit on? Mainline? Some branch in block.git? It was just master in -git. But looks like I did miss two spots, I've updated the series here and will send out a v2: https://git.kernel.dk/cgit/linux-block/log/?h=iter-ubuf -- Jens Axboe
