* Re: CLONE_IO documentation [not found] ` <20080414171330.GP12774-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> @ 2008-11-19 22:30 ` Michael Kerrisk [not found] ` <cfd18e0f0811191430u761e58f3i98b169f6e8d09bc9-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 0 siblings, 1 reply; 3+ messages in thread From: Michael Kerrisk @ 2008-11-19 22:30 UTC (permalink / raw) To: Jens Axboe Cc: Andrew Morton, Linux Kernel Mailing List, linux-man-u79uwXL29TY76Z2rM5mHXA Hi Jens, Following up after a long time on this: On Mon, Apr 14, 2008 at 12:13 PM, Jens Axboe <jens.axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote: > On Mon, Apr 14 2008, Michael Kerrisk wrote: >> Hi Jens, >> >> Could you supply some text describing CLONE_IO suitable for inclusion >> in the clone.2 man page? >> ( http://www.kernel.org/doc/man-pages/online/pages/man2/clone.2.html >> ). In that text it would be helpful to explain what an "I/O context" >> is. > > Sure, I'll see if I can come up with something. Or perhaps you can help > me a bit, being the writer ;-) > > If the CLONE_IO flag is set, the process will share the same io context. > The I/O context is the I/O scope of the disk scheduler. So if you think > of the I/O context as what the I/O scheduler uses to map to a process, > when CLONE_IO is set multiple processes will map to the same I/O context > and will be treated as one by the I/O scheduler. What this means is that > they get to share disk time. For the anticipatory and CFQ scheduler, if > process A and process B share I/O context, they will be allowed to > interleave their disk access. So if you have several threads doing I/O > on behalf of the same process (aio_read(), for instance), they should > set CLONE_IO to get better I/O performance with CFQ and AS. > > A man page should not mention the specific schedulers, just mention that > it'll improve the information available to the kernel and the > performance of the app for the scenario described. In practice, it'll > only really apply to CFQ and AS. For deadline and noop, they'll be > essentially zero difference as they have no concept of I/O contexts. I took your text as a base but did some reworking, so *please check the following carefully*, and let me know if there are things to change and/or add: CLONE_IO (since Linux 2.4.25) If CLONE_IO is set, then the new process shares an I/O context with the calling process. If this flag is not set, then (as with fork(2)) the new process has its own I/O context. The I/O context is the I/O scope of the disk scheduler (i.e, what the I/O scheduler uses to model scheduling of a process's I/O). If processes share the same I/O con- text, they are treated as one by the I/O scheduler. As a consequence, they get to share disk time. For some I/O schedulers, if two processes share an I/O context, they will be allowed to interleave their disk access. If several threads are doing I/O on behalf of the same process (aio_read(3), for instance), they should employ CLONE_IO to get better I/O performance. If the kernel is not configured with the CONFIG_BLOCK option, this flag is a no-op. The patch against clone.2 is below. Thanks, Michael --- a/man2/clone.2 +++ b/man2/clone.2 @@ -224,6 +223,36 @@ Calls to .BR umask (2) performed later by one of the processes do not affect the other process. .TP +.BR CLONE_IO " (since Linux 2.4.25)" +If +.B CLONE_IO +is set, then the new process shares an I/O context with +the calling process. +If this flag is not set, then (as with +.BR fork (2)) +the new process has its own I/O context. + +.\" The following based on text from Jens Axboe +The I/O context is the I/O scope of the disk scheduler (i.e, +what the I/O scheduler uses to model scheduling of a process's I/O). +If processes share the same I/O context, +they are treated as one by the I/O scheduler. +As a consequence, they get to share disk time. +For some I/O schedulers, +.\" the anticipatory and CFQ scheduler +if two processes share an I/O context, +they will be allowed to interleave their disk access. +If several threads are doing I/O on behalf of the same process +.RB ( aio_read (3), +for instance), they should employ +.BR CLONE_IO +to get better I/O performance. +.\" with CFQ and AS. + +If the kernel is not configured with the +.B CONFIG_BLOCK +option, this flag is a no-op. +.TP .BR CLONE_NEWIPC " (since Linux 2.4.19)" If .B CLONE_NEWIPC -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 3+ messages in thread
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* Re: CLONE_IO documentation [not found] ` <cfd18e0f0811191430u761e58f3i98b169f6e8d09bc9-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> @ 2008-11-20 7:48 ` Jens Axboe [not found] ` <20081120074803.GC26308-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> 0 siblings, 1 reply; 3+ messages in thread From: Jens Axboe @ 2008-11-20 7:48 UTC (permalink / raw) To: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w Cc: Andrew Morton, Linux Kernel Mailing List, linux-man-u79uwXL29TY76Z2rM5mHXA On Wed, Nov 19 2008, Michael Kerrisk wrote: > Hi Jens, > > Following up after a long time on this: > > On Mon, Apr 14, 2008 at 12:13 PM, Jens Axboe <jens.axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote: > > On Mon, Apr 14 2008, Michael Kerrisk wrote: > >> Hi Jens, > >> > >> Could you supply some text describing CLONE_IO suitable for inclusion > >> in the clone.2 man page? > >> ( http://www.kernel.org/doc/man-pages/online/pages/man2/clone.2.html > >> ). In that text it would be helpful to explain what an "I/O context" > >> is. > > > > Sure, I'll see if I can come up with something. Or perhaps you can help > > me a bit, being the writer ;-) > > > > If the CLONE_IO flag is set, the process will share the same io context. > > The I/O context is the I/O scope of the disk scheduler. So if you think > > of the I/O context as what the I/O scheduler uses to map to a process, > > when CLONE_IO is set multiple processes will map to the same I/O context > > and will be treated as one by the I/O scheduler. What this means is that > > they get to share disk time. For the anticipatory and CFQ scheduler, if > > process A and process B share I/O context, they will be allowed to > > interleave their disk access. So if you have several threads doing I/O > > on behalf of the same process (aio_read(), for instance), they should > > set CLONE_IO to get better I/O performance with CFQ and AS. > > > > A man page should not mention the specific schedulers, just mention that > > it'll improve the information available to the kernel and the > > performance of the app for the scenario described. In practice, it'll > > only really apply to CFQ and AS. For deadline and noop, they'll be > > essentially zero difference as they have no concept of I/O contexts. > > I took your text as a base but did some reworking, so *please check > the following carefully*, and let me know if there are things to > change and/or add: > > CLONE_IO (since Linux 2.4.25) > If CLONE_IO is set, then the new process shares an I/O > context with the calling process. If this flag is not > set, then (as with fork(2)) the new process has its own > I/O context. > > The I/O context is the I/O scope of the disk scheduler > (i.e, what the I/O scheduler uses to model scheduling of > a process's I/O). If processes share the same I/O con- > text, they are treated as one by the I/O scheduler. As > a consequence, they get to share disk time. For some > I/O schedulers, if two processes share an I/O context, > they will be allowed to interleave their disk access. > If several threads are doing I/O on behalf of the same > process (aio_read(3), for instance), they should employ > CLONE_IO to get better I/O performance. > > If the kernel is not configured with the CONFIG_BLOCK > option, this flag is a no-op. > > The patch against clone.2 is below. That looks good, but you typoed the kernel version - it should read 'since 2.6.25' :-) -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 3+ messages in thread
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* Re: CLONE_IO documentation [not found] ` <20081120074803.GC26308-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> @ 2008-11-20 11:52 ` Michael Kerrisk 0 siblings, 0 replies; 3+ messages in thread From: Michael Kerrisk @ 2008-11-20 11:52 UTC (permalink / raw) To: Jens Axboe Cc: Andrew Morton, Linux Kernel Mailing List, linux-man-u79uwXL29TY76Z2rM5mHXA On Thu, Nov 20, 2008 at 2:48 AM, Jens Axboe <jens.axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote: > On Wed, Nov 19 2008, Michael Kerrisk wrote: >> Hi Jens, >> >> Following up after a long time on this: >> >> On Mon, Apr 14, 2008 at 12:13 PM, Jens Axboe <jens.axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote: >> > On Mon, Apr 14 2008, Michael Kerrisk wrote: >> >> Hi Jens, >> >> >> >> Could you supply some text describing CLONE_IO suitable for inclusion >> >> in the clone.2 man page? >> >> ( http://www.kernel.org/doc/man-pages/online/pages/man2/clone.2.html >> >> ). In that text it would be helpful to explain what an "I/O context" >> >> is. >> > >> > Sure, I'll see if I can come up with something. Or perhaps you can help >> > me a bit, being the writer ;-) >> > >> > If the CLONE_IO flag is set, the process will share the same io context. >> > The I/O context is the I/O scope of the disk scheduler. So if you think >> > of the I/O context as what the I/O scheduler uses to map to a process, >> > when CLONE_IO is set multiple processes will map to the same I/O context >> > and will be treated as one by the I/O scheduler. What this means is that >> > they get to share disk time. For the anticipatory and CFQ scheduler, if >> > process A and process B share I/O context, they will be allowed to >> > interleave their disk access. So if you have several threads doing I/O >> > on behalf of the same process (aio_read(), for instance), they should >> > set CLONE_IO to get better I/O performance with CFQ and AS. >> > >> > A man page should not mention the specific schedulers, just mention that >> > it'll improve the information available to the kernel and the >> > performance of the app for the scenario described. In practice, it'll >> > only really apply to CFQ and AS. For deadline and noop, they'll be >> > essentially zero difference as they have no concept of I/O contexts. >> >> I took your text as a base but did some reworking, so *please check >> the following carefully*, and let me know if there are things to >> change and/or add: >> >> CLONE_IO (since Linux 2.4.25) >> If CLONE_IO is set, then the new process shares an I/O >> context with the calling process. If this flag is not >> set, then (as with fork(2)) the new process has its own >> I/O context. >> >> The I/O context is the I/O scope of the disk scheduler >> (i.e, what the I/O scheduler uses to model scheduling of >> a process's I/O). If processes share the same I/O con- >> text, they are treated as one by the I/O scheduler. As >> a consequence, they get to share disk time. For some >> I/O schedulers, if two processes share an I/O context, >> they will be allowed to interleave their disk access. >> If several threads are doing I/O on behalf of the same >> process (aio_read(3), for instance), they should employ >> CLONE_IO to get better I/O performance. >> >> If the kernel is not configured with the CONFIG_BLOCK >> option, this flag is a no-op. >> >> The patch against clone.2 is below. > > That looks good, Okay -- thanks. > but you typoed the kernel version - it should read > 'since 2.6.25' :-) Will fix; thanks. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 3+ messages in thread
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2008-11-19 22:30 ` CLONE_IO documentation Michael Kerrisk
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