Date: Sat, 3 Sep 2022 03:41:06 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Alan Somers <asomers@freebsd.org> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org>, Alexander Motin <mav@FreeBSD.org>, Mateusz Guzik <mjguzik@gmail.com> Subject: Re: RFC: multiple concurrent I/O ops for copy_file_range(2) Message-ID: <YQXPR01MB4150346FF77D5B73574E9444DD7D9@YQXPR01MB4150.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <CAOtMX2jm7vg_38oV36UZ3LrJy-6hCF0Utk=dGCbfdsmr7sq9gQ@mail.gmail.com> References: <YQXPR01MB41506C61D9936C01072F6373DD7D9@YQXPR01MB4150.CANPRD01.PROD.OUTLOOK.COM> <CAOtMX2jm7vg_38oV36UZ3LrJy-6hCF0Utk=dGCbfdsmr7sq9gQ@mail.gmail.com>
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Alan Somers <asomers@freebsd.org> wrote: >On Fri, Sep 2, 2022 at 9:11 PM Rick Macklem <rmacklem@uoguelph.ca> wrote: >> >> Hi, >> >> A recent discussion involving copy_file_range(2) performance >> included a suggestion that, maybe, copying of subranges >> should be done concurrently. >> >> Although I cannot be 100% sure, I think that this would >> involve using multiple kernel threads (taskqueue or similar) >> to issue I/O operations on the file system(s) for blocks >> (of f_iosize maybe?) concurrently, to improve performance. >> >> Doing this in a system call is unusual, to say the least but, then, >> copy_file_range(2) is an unusual system call to begin with. >> >> I have not attempted to code this up as of yet. >> >> So, what do others think of this idea? >> >> rick > >I'm skeptical. Is the intention to speed up copying on file systems >that do or don't have an efficient VOP_COPY_FILE_RANGE implementation? I suppose so. In particular, when the input and output files are on different file systems, a custom VOP_COPY_FILE_RANGE() cannot be used. > For those that don't, I don't see any point in trying to beat the >speed of the old cp(1). Apart from the problems that we've seen >around hole size, does the copy_file-range-enabled cp match the older >cp's performance? Well, the discussion starts here: https://lists.freebsd.org/archives/dev-commits-src-main/2022-August/009067.html For some reason, there seems to be missing entries. I recall replying to the one that suggested concurrent I/O operations (by mav@, I think?) that I would post here asking about it. (I've cc'd mav@, in case he wishes to comment further.) I do agree that doing some performance evaluation of cp(1) would be useful. --> The thread seemed to suggest (I'm no ZFS guy) that mmap'd copying does not help for ZFS and that doing copy_file_range(2) for small files instead of the mmap'd copying might make sense. --> Then there was mention of having copy_file_range(2) do concurrent copying of blocks, which precipitated the email. rickhelp
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