add Shaohua to the cc list, On 04/03/2012 11:37 PM, Vivek Goyal wrote: > On Tue, Apr 03, 2012 at 06:41:37AM +0800, Tao Ma wrote: >> On 04/03/2012 06:25 AM, Vivek Goyal wrote: >>> On Tue, Apr 03, 2012 at 06:20:10AM +0800, Tao Ma wrote: >>> >>> [..] >>>>> Yeah, just add config and stat files prefixed with the name of the new >>>>> blkcg policy. >>>> OK, I will add a new config file for it. >>> >>> Only if CFQ could be modified to add one iops mode, flippable through a >>> sysfs tunable, things will be much simpler. You will not have to add a >>> new IO scheduler, no new configuration/stat files in blkcg (which is >>> already crowded now). >>> >>> I don't think anybody has shown the code that why CFQ can't be modified >>> to support iops mode. >> Yes, I have thought of it, but it seems to me that time slice is deeply >> involved within the cfq(even current cfq's iops mode has used time slice >> to calculate). So I don't think it is feasible for me to change it. And >> cfq works perfectly well for sas/sata environment and the code is quite >> stable, more codes and more complicate algorithm does mean more bugs. So >> I guess a new iops based scheduler is easy and not intrusive for the >> user(since he can choose whether to use it or not). > > Ok, let me take one step back. > > - What's the goal of iops based scheduler. In what kind of workload and > storage it is going to help. > > - Can't we just set the slice_idle=0 and "quantum" to some high value > say "64" or "128" and achieve similar results to iops based scheduler? yes, I should say cfq with slice_idle = 0 works well in most cases. But if it comes to blkcg with ssd, it is really a disaster. You know, cfq has to choose between different cgroups, so even if you choose 1ms as the service time for each cgroup(actually in my test, only >2ms can work reliably). the latency for some requests(which have been sent by the user while not submitting to the driver) is really too much for the application. I don't think there is a way to resolve it in cfq. > > In theory, above will cut down on idling and try to provide fairness in > terms of time. I thought fairness in terms of time is most fair. The > most common problem is measurement of time is not attributable to > individual queue in an NCQ hardware. I guess that throws time measurement > of out the window until and unless we have a better algorithm to measure > time in NCQ environment. > > I guess then we can just replace time with number of requests dispatched > from a process queue. Allow it to dispatch requests for some time and > then schedule it out and put it back on service tree and charge it > according to its weight. As I have said, in this case, the minimal time(1ms) multiple the group number is too much for a ssd. If we can use iops based scheduler, we can use iops_weight for different cgroups and switch cgroup according to this number. So all the applications can have a moderate response time which can be estimated. btw, I have talked with Shaohua in LSF and we made a consensus that I will continue his work and try to add cgroup support to it. Thanks Tao > > This all works only if we have right workload. The workloads which are > not doing dependent reads and can keep the disk busy continuously. If > there is think time involved, and we do not idle, process will lose its > share and whole scheme of trying to differentiate between processes will > become ineffective. > > So if you have come with a better algorith which can keep track of iops > without idling and still provide service differentiation for common > workloads, it will be interesting. > > Thanks > Vivek > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
