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Open Source and information security mailing list archives
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Date: Fri, 29 Mar 2013 16:20:19 -0700 From: Tim Chen <tim.c.chen@...ux.intel.com> To: Linus Torvalds <torvalds@...ux-foundation.org>, Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...nel.org> Cc: Alex Shi <alex.shi@...el.com>, Changlong Xie <changlongx.xie@...el.com>, linux-kernel <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org> Subject: Load balancing behavior for sched autogroup During our testings of 3.8 kernel, we noticed that after the patch Revert "sched: Update_cfs_shares at period edge" (commit 17bc14b7), the load between the sockets or larger system can have large imbalance. For example, for a 4 socket Westmere-EX (10 cores/socket), we notice the loadings between the sockets can differ by more than a factor of 4. We did a simple experiment that kicks off 29 simple processes that execute a tight loop. We noticed socket 3 is already starting to schedule on hyperthreaded cpus (13 loaded cpus) while socket 1 still have lots of idle cores (3 loaded cpus). Before the patch, the load was evenly distributed across sockets. If I turn off CONFIG_SCHED_AUTOGROUP,the loads are also distributed evenly. (load on cpus, running on 4) socket 0 1 2 3 --------------------------------------------------------------------------------------------- cpu: 0-3 0.00 0.00 0.00 99.00 cpu: 4-7 0.00 0.00 0.00 99.20 cpu: 8-11 0.00 0.00 0.00 99.00 cpu: 12-15 99.20 0.00 0.00 0.00 cpu: 16-19 0.00 0.00 0.00 99.00 cpu: 20-23 0.00 0.00 0.00 0.00 cpu: 24-27 0.00 0.00 0.00 0.00 cpu: 28-31 0.00 0.00 0.00 0.00 cpu: 32-35 99.20 0.00 0.00 99.00 cpu: 36-39 99.20 99.40 99.20 0.00 cpu: 40-43 0.00 99.40 99.40 99.20 cpu: 44-47 0.00 99.40 99.40 99.20 cpu: 48-51 99.40 0.00 99.40 99.20 cpu: 52-55 99.20 0.00 99.40 99.20 cpu: 56-59 0.00 0.00 99.40 99.40 cpu: 60-63 0.00 0.00 0.00 99.00 cpu: 64-67 0.00 0.00 0.00 99.40 cpu: 68-71 0.00 0.00 0.00 99.40 cpu: 72-75 99.40 0.00 0.00 0.00 cpu: 76-79 99.40 0.00 0.00 0.00 --------------------------------------------------------------------------------------------- Loaded cpus 7 3 6 13 Is this the intended behavior of sched autogroup? I'm a bit surprised that we are reserving this much cpu bandwidth for very low load processes (or interactive processes) in other groups. So should the sched autogroup config option be turned off by default for server system, when we are not concerned about interactivity but want to maximize throughput by balancing out the load? Thanks for clarifying. Tim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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