[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] Add a timer mode that disables pending missed ticks
Hi Dan, I had to put that port aside with other pressing issues here. I will try to get the port done in the next couple of days. Is that soon enough for 3.1.3? To see the error with timer_mode=2(=SYNC=no missed ticks pending) you probably need to over commit the physical processors with virtual processors, say 2:1, and then load up all the virtual processors. Regards, Dave Dan Magenheimer wrote: Hi Dave -- Did you get your correction ported? If so, it would be nice to see this get into 3.1.3. Note that I just did some very limited testing with timer_mode=2(=SYNC=no missed ticks pending) on tip of xen-3.1-testing (64-bit Linux hv guest) and the worst error I've seen so far is 0.012%. But I haven't tried any exotic loads, just LTP. Thanks, Dan-----Original Message----- From: Dave Winchell [mailto:dwinchell@xxxxxxxxxxxxxxx] Sent: Wednesday, December 19, 2007 12:33 PM To: dan.magenheimer@xxxxxxxxxx Cc: Keir Fraser; Shan, Haitao; xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Jiang, Yunhong; Dave WinchellSubject: Re: [Xen-devel] [PATCH] Add a timer mode that disables pendingmissed ticks Dan,I did some testing with the constant tsc offset SYNC method (now calledno_missed_ticks_pending)and found the error to be very high, much larger than 1 %, as I recall. I have not had a chance to submit a correction. I will try to do it laterthis week or the first week in January. My version of constant tsc offset SYNC methodproduces .02 % error, so I just need to port that into the current code.The error you got for both of those kernels is what I would expect for the default mode, delay_for_missed_ticks. I'll let Keir answer on how to set the time mode. Regards, Dave Dan Magenheimer wrote:about 0.2% with no load. This was xen-unstable tip today with no options specified. 32-bit was about 0.01%.Anyone make measurements on the final patch?I just ran a 64-bit RHEL5.1 pvm kernel and saw a loss ofI think I missed something... how do I run the variousaccounting choices and which ones are known to be appropriate for which kernels?Thanks, Dan-----Original Message----- From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx]On Behalf OfKeir FraserSent: Thursday, December 06, 2007 4:57 AM To: Dave Winchell Cc: Shan, Haitao; xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Jiang, Yunhong Subject: Re: [Xen-devel] [PATCH] Add a timer mode that disables pending missed ticks Please take a look at xen-unstable changeset 16545. -- KeirOn 26/11/07 20:57, "Dave Winchell"<dwinchell@xxxxxxxxxxxxxxx> wrote:Keir, The accuracy data I've collected for i/o loads for the various time protocols follows. In addition, the data for cpu loads is shown. The loads labeled cpu and i/o-8 are on an 8 processor AMD box. Two guests, red hat and sles 64 bit, 8 vcpu each. The cpu load is usex -e36 on each guest. (usex is available at http://people.redhat.com/anderson/usex.) i/o load is 8 instances of dd if=/dev/hda6 of=/dev/null. The loads labeled i/o-32 are 32 instances of dd. Also, these are run on 4 cpu AMD box. In addition, there is an idle rh-32bit guest. All three guests are 8vcpu. The loads labeled i/o-4/32 are the same as i/o-32 except that the redhat-64 guest has 4 instances of dd. Date Duration Protocol sles, rhat error load 11/07 23 hrs 40 min ASYNC -4.96 sec, +4.42 sec -.006%, +.005% cpu 11/09 3 hrs 19 min ASYNC -.13 sec, +1.44 sec, -.001%, +.012% cpu 11/08 2 hrs 21 min SYNC -.80 sec, -.34 sec, -.009%, -.004% cpu 11/08 1 hr 25 min SYNC -.24 sec, -.26 sec, -.005%, -.005% cpu 11/12 65 hrs 40 min SYNC -18 sec, -8 sec, -.008%, -.003% cpu 11/08 28 min MIXED -.75 sec, -.67 sec -.045%, -.040% cpu 11/08 15 hrs 39 min MIXED -19. sec,-17.4 sec, -.034%, -.031% cpu 11/14 17 hrs 17 min ASYNC -6.1 sec,-55.7 sec, -.01%, -.09% i/o-8 11/15 2 hrs 44 min ASYNC -1.47 sec,-14.0 sec, -.015% -.14% i/o-8 11/13 15 hrs 38 min SYNC -9.7 sec,-12.3 sec, -.017%, -.022% i/o-8 11/14 48 min SYNC - .46 sec, - .48 sec, -.017%, -.018% i/o-8 11/14 4 hrs 2 min MIXED -2.9 sec, -4.15 sec, -.020%, -.029% i/o-8 11/20 16 hrs 2 min MIXED -13.4 sec,-18.1 sec, -.023%, -.031% i/o-8 11/21 28 min MIXED -2.01 sec, -.67 sec, -.12%, -.04% i/o-32 11/21 2 hrs 25 min SYNC -.96 sec, -.43 sec, -.011%, -.005% i/o-32 11/21 40 min ASYNC -2.43 sec, -2.77 sec -.10%, -.11% i/o-32 11/26 113 hrs 46 min MIXED -297. sec, 13. sec -.07%, .003% i/o-4/32 11/26 4 hrs 50 min SYNC -3.21 sec, 1.44 sec, -.017%, .01% i/o-4/32 Overhead measurements: Progress in terms of number of passes through a fixedsystem workloadon an 8 vcpu red hat with an 8 vcpu sles idle. The workload was usex -b48. ASYNC 167 min 145 passes .868 passes/min SYNC 167 min 144 passes .862 passes/min SYNC 1065 min 919 passes .863 passes/min MIXED 221 min 196 passes .887 passes/min Conclusions: The only protocol which meets the .05% accuracy requirement for ntp tracking under the loads above is the SYNC protocol. The worst case accuracies forSYNC, MIXED,and ASYNC are .022%, .12%, and .14%, respectively. We could reduce the cost of the SYNC method by onlyscheduling the extrawakeups if a certain number of ticks are missed. Regards, Dave Keir Fraser wrote:On 9/11/07 19:22, "Dave Winchell"<dwinchell@xxxxxxxxxxxxxxx> wrote:Since I had a high error (~.03%) for the ASYNC method acouple of days ago,I ran another ASYNC test. I think there may have been something wrong with the code I used a couple of days ago forASYNC. It may have beenmissing the immediate delivery of interrupt after contextswitch in.My results indicate that either SYNC or ASYNC giveacceptable accuracy,each running consistently around or under .01%. MIXED hasa fairly higherror of greater than .03%. Probably too close to .05% ntpthreshold for comfort.I don't have an overnight run with SYNC. I plan to leaveSYNC runningover the weekend. If you'd rather I can leave MIXEDrunning instead.It may be too early to pick the protocol and I can runmore overnight testsnext week.I'm a bit worried about any unwanted side effects of theSYNC+run_timerapproach -- e.g., whether timer wakeups will cause highersystem-wide CPUcontention. I find it easier to think through theimplications of ASYNC. I'msurprised that MIXED loses time, and is less accurate thanASYNC. Perhaps itdelivers more timer interrupts than the other approaches,and each interruptevent causes a small accumulated error? Overall I would consider MIXED and ASYNC as favourites andif the latter isactually more accurate then I can simply revert the changeset that implemented MIXED. Perhaps rather than running more of the same workloads youcould try idleVCPUs and I/O bound VCPUs (e.g., repeated large disc readsto /dev/null)? Wedon't have any data on workloads that aren't CPU bound, sothat's really anobvious place to put any further effort imo. -- Keir_______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |