Hi, to be honest, i never made real benchmarks about that. But to me, i doubt that the higher frequency of a cpu will have a "real" impact on ceph's performance. I mean, yes, mathematically, just like Wade pointed out, its true. > frequency = < latency But when we compare CPU's of the same model, with different frequencies. How much time ( in nano seconds ), do we save ? I mean i have really no numbers here. But the difference between a 2,1 GHz and a 2,9 GHz ( Low End Xeon E5 / High End Xeon E5 ) ( when it comes to delay in "memory/what ever" allocation ), will be, inside an Linux OS, quiet small. And i mean nano seconds tiny/non existing small. But again, thats just my guess. Of course, if we talk about complete different CPU Models ( E5 vs. I7 vs. AMD vs. what ever ) we will have different 1st/2nd level Caches in CPU, different Architecture/RAM/everything. But we are talking here about pure frequency issues. So we compare identical CPU Models, just with different frequencies. And there, the difference, especially inside an OS and inside a productive environment must be nearly not existing. I can not imagine how much an OSD / HDD needs to be hammered, that a server is in general not totally overloaded and that the higher frequency will make a measureable difference. ---- But again, i have here no numbers/benchmarks that could proove this pure theory of mine. In the very end, more cores will usually mean more GHz frequency in sum. So maybe the whole discussion is very theoretically, because usually we wont run in a situation where we have to choose frequency vs. cores. Simply because more cores always means more frequency in sum. Except you compare totally different cpu models and generations, and this is even more worst theoretically and maybe pointless since the different cpu generations have totally different inner architecture which has a great impact in overall performance ( aside from numbers of frequency and cores ). -- Mit freundlichen Gruessen / Best regards Oliver Dzombic IP-Interactive mailto:info@xxxxxxxxxxxxxxxxx Anschrift: IP Interactive UG ( haftungsbeschraenkt ) Zum Sonnenberg 1-3 63571 Gelnhausen HRB 93402 beim Amtsgericht Hanau Geschäftsführung: Oliver Dzombic Steuer Nr.: 35 236 3622 1 UST ID: DE274086107 Am 20.01.2016 um 14:14 schrieb Wade Holler: > Great commentary. > > While it is fundamentally true that higher clock speed equals lower > latency, I'm my practical experience we are more often interested in > latency at the concurrency profile of the applications. > > So in this regard I favor more cores when I have to choose, such that we > can support more concurrent operations at a queue depth of 0. > > Cheers > Wade > On Wed, Jan 20, 2016 at 7:58 AM Jan Schermer <jan@xxxxxxxxxxx > <mailto:jan@xxxxxxxxxxx>> wrote: > > I'm using Ceph with all SSDs, I doubt you have to worry about speed that > much with HDD (it will be abysmall either way). > With SSDs you need to start worrying about processor caches and memory > colocation in NUMA systems, linux scheduler is not really that smart > right now. > Yes, the process will get its own core, but it might be a different > core every > time it spins up, this increases latencies considerably if you start > hammering > the OSDs on the same host. > > But as always, YMMV ;-) > > Jan > > > > On 20 Jan 2016, at 13:28, Oliver Dzombic <info@xxxxxxxxxxxxxxxxx > <mailto:info@xxxxxxxxxxxxxxxxx>> wrote: > > > > Hi Jan, > > > > actually the linux kernel does this automatically anyway ( sending new > > processes to "empty/low used" cores ). > > > > A single scrubbing/recovery or what ever process wont take more than > > 100% CPU ( one core ) because technically this processes are not > able to > > run multi thread. > > > > Of course, if you configure your ceph to have ( up to ) 8 backfill > > processes, then 8 processes will start, which can utilize ( up to ) 8 > > CPU cores. > > > > But still, the single process wont be able to use more than one > cpu core. > > > > --- > > > > In a situation where you have 2x E5-2620v3 for example, you have 2x 6 > > Cores x 2 HT Units = 24 Threads ( vCores ). > > > > So if you use inside such a system 24 OSD's every OSD will have ( > > mathematically ) its "own" CPU Core automatically. > > > > Such a combination will perform better compared if you are using 1x E5 > > CPU with a much higher frequency ( but still the same amout of > cores ). > > > > This kind of CPU's are so fast, that the physical HDD ( no matter if > > SAS/SSD/ATA ) will not be able to overload the cpu ( no matter > which cpu > > you use of this kind ). > > > > Its like if you are playing games. If the game is running smooth, it > > does not matter if its running on a 4 GHz machine on 40% > utilization or > > on a 2 GHz machine with 80% utilization. Is running smooth, it can not > > do better :-) > > > > So if your data is coming as fast as the HDD can physical deliver it, > > its not important if the cpu runs with 2, 3, 4, 200 Ghz. Its > already the > > max of what the HDD can deliver. > > > > So as long as the HDD's dont get faster, the CPU's does not need to be > > faster. > > > > The Ceph storage is usually just delivering data, not running a > > commercial webserver/what ever beside that. > > > > So if you are deciding what CPU you have to choose, you only have to > > think about how fast your HDD devices are. So that the CPU does not > > become the bottleneck. > > > > And the more cores you have, the lower is the chance, that different > > requests will block each other. > > > > ---- > > > > So all in all, Core > Frequency, always. ( As long as you use > fast/up to > > date CPUs ). If you are using old cpu's, of course you have to > make sure > > that the performance of the cpu ( which does by the way not only > depend > > on the frequency ) is sufficient that its not breaking the HDD > data output. > > > > > > > > -- > > Mit freundlichen Gruessen / Best regards > > > > Oliver Dzombic > > IP-Interactive > > > > mailto:info@xxxxxxxxxxxxxxxxx <mailto:info@xxxxxxxxxxxxxxxxx> > > > > Anschrift: > > > > IP Interactive UG ( haftungsbeschraenkt ) > > Zum Sonnenberg 1-3 > > 63571 Gelnhausen > > > > HRB 93402 beim Amtsgericht Hanau > > Geschäftsführung: Oliver Dzombic > > > > Steuer Nr.: 35 236 3622 1 > > UST ID: DE274086107 > > > > > > Am 20.01.2016 um 13:10 schrieb Jan Schermer: > >> This is very true, but do you actually exclusively pin the cores > to the OSD daemons so they don't interfere? > >> I don't think may people do that, it wouldn't work with more than > a handful of OSDs. > >> The OSD might typicaly only need <100% of one core, but during > startup or some reshuffling it's beneficial > >> to allow it to get more (>400%), and that will interfere with > whatever else was pinned there... > >> > >> Jan > >> > >>> On 20 Jan 2016, at 13:07, Oliver Dzombic <info@xxxxxxxxxxxxxxxxx > <mailto:info@xxxxxxxxxxxxxxxxx>> wrote: > >>> > >>> Hi, > >>> > >>> Cores > Frequency > >>> > >>> If you think about recovery / scrubbing tasks its better when a > cpu core > >>> can be assigned to do this. > >>> > >>> Compared to a situation where the same cpu core needs to > recovery/scrub > >>> and still deliver the productive content at the same time. > >>> > >>> The more you can create a situation where an osd has its "own" > cpu core, > >>> the better it is. Modern CPU's are anyway so fast, that even > SSDs cant > >>> run the CPU's to their limit. > >>> > >>> -- > >>> Mit freundlichen Gruessen / Best regards > >>> > >>> Oliver Dzombic > >>> IP-Interactive > >>> > >>> mailto:info@xxxxxxxxxxxxxxxxx <mailto:info@xxxxxxxxxxxxxxxxx> > >>> > >>> Anschrift: > >>> > >>> IP Interactive UG ( haftungsbeschraenkt ) > >>> Zum Sonnenberg 1-3 > >>> 63571 Gelnhausen > >>> > >>> HRB 93402 beim Amtsgericht Hanau > >>> Geschäftsführung: Oliver Dzombic > >>> > >>> Steuer Nr.: 35 236 3622 1 > >>> UST ID: DE274086107 > >>> > >>> > >>> Am 20.01.2016 um 10:01 schrieb Götz Reinicke - IT Koordinator: > >>>> Hi folks, > >>>> > >>>> we plan to use more ssd OSDs in our first cluster layout > instead of SAS > >>>> osds. (more IO is needed than space) > >>>> > >>>> short question: What would influence the performance more? more > Cores or > >>>> more GHz/Core. > >>>> > >>>> Or is it as always: Depeds on the total of > OSDs/nodes/repl-level/etc ... :) > >>>> > >>>> If needed, I can give some more detailed information on the layout. > >>>> > >>>> Thansk for feedback . Götz > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> ceph-users mailing list > >>>> ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> > >>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > >>>> > >>> _______________________________________________ > >>> ceph-users mailing list > >>> ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> > >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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