Messages in this thread | | | Date | Thu, 5 Nov 2009 09:39:14 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCH 02/20] blkio: Change CFQ to use CFS like queue time stamps |
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On Wed, Nov 04, 2009 at 06:44:28PM -0800, Divyesh Shah wrote: > On Wed, Nov 4, 2009 at 8:37 AM, Vivek Goyal <vgoyal@redhat.com> wrote: > > On Wed, Nov 04, 2009 at 09:30:34AM -0500, Jeff Moyer wrote: > >> Vivek Goyal <vgoyal@redhat.com> writes: > >> > > > > Thanks for the review Jeff. > > > >> > o Currently CFQ provides priority scaled time slices to processes. If a process > >> > does not use the time slice, either because process did not have sufficient > >> > IO to do or because think time of process is large and CFQ decided to disable > >> > idling, then processes looses it time slice share. > >> ^^^^^^ > >> loses > >> > > > > Will fix it. > > > >> > o One possible way to handle this is implement CFS like time stamping of the > >> > cfq queues and keep track of vtime. Next queue for execution will be selected > >> > based on the one who got lowest vtime. This patch implemented time stamping > >> > mechanism of cfq queues based on disk time used. > >> > > >> > o min_vdisktime represents the minimum vdisktime of the queue, either being > >> ^^^^^ > >> > serviced or leftmost element on the serviec tree. > >> > >> queue or service tree? The latter seems to make more sense to me. > > > > Yes, it should be service tree. Will fix it. > > > >> > >> > +static inline u64 > >> > +cfq_delta_fair(unsigned long delta, struct cfq_queue *cfqq) > >> > +{ > >> > + const int base_slice = cfqq->cfqd->cfq_slice[cfq_cfqq_sync(cfqq)]; > >> > + > >> > + return delta + (base_slice/CFQ_SLICE_SCALE * (cfqq->ioprio - 4)); > >> > +} > >> > >> cfq_scale_delta might be a better name. > >> > > > > cfq_scale_delta sounds good. Will use it in next version. > > > >> > >> > +static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime) > >> > +{ > >> > + s64 delta = (s64)(vdisktime - min_vdisktime); > >> > + if (delta > 0) > >> > + min_vdisktime = vdisktime; > >> > + > >> > + return min_vdisktime; > >> > +} > >> > + > >> > +static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime) > >> > +{ > >> > + s64 delta = (s64)(vdisktime - min_vdisktime); > >> > + if (delta < 0) > >> > + min_vdisktime = vdisktime; > >> > + > >> > + return min_vdisktime; > >> > +} > >> > >> Is there a reason you've reimplemented min and max? > > > > I think you are referring to min_t and max_t. Will these macros take care > > of wrapping too? > > > > For example, if I used min_t(u64, A, B), then unsigned comparision will > > not work right wrapping has just taken place for any of the A or B. So if > > A=-1 and B=2, then min_t() would return B as minimum. This is not right > > in our case. > > > > If we do signed comparison (min_t(s64, A, B)), that also seems to be > > broken in another case where a value of variable moves from 63bits to 64bits, > > (A=0x7fffffffffffffff, B=0x8000000000000000). Above will return B as minimum but > > in our scanario, vdisktime will progress from 0x7fffffffffffffff to > > 0x8000000000000000 and A should be returned as minimum (unsigned > > comparison). > > Can you define and use u64 versions of time_before() and time_after() > (from include/linux/jiffies.h) for your comparisons? These take care > of wrapping as well. Maybe call them timestamp_before()/after(). > > > > > Hence I took these difnitions from CFS. > > Also if these are exactly the same and you decide to continue using > these, can we move them to a common header file (time.h or maybe add a > vtime.h) and reuse? >
Ok. I will look into it. Sharing the function between CFS scheduler and CFQ scheduler.
Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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