Messages in this thread | | | From | Dietmar Eggemann <> | Subject | Re: [PATCH v2 2/9] sched/debug: Make sd->flags sysctl read-only | Date | Thu, 19 Mar 2020 10:07:21 +0100 |
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On 11.03.20 19:15, Valentin Schneider wrote: > Writing to the sysctl of a sched_domain->flags directly updates the value of > the field, and goes nowhere near update_top_cache_domain(). This means that > the cached domain pointers can end up containing stale data (e.g. the > domain pointed to doesn't have the relevant flag set anymore). > > Explicit domain walks that check for flags will be affected by > the write, but this won't be in sync with the cached pointers which will > still point to the domains that were cached at the last sched_domain > build. > > In other words, writing to this interface is playing a dangerous game. It > could be made to trigger an update of the cached sched_domain pointers when > written to, but this does not seem to be worth the trouble. Make it > read-only.
As long as I don't change SD flags for which cached SD pointers exist (SD_SHARE_PKG_RESOURCES, SD_NUMA, SD_ASYM_PACKING or SD_ASYM_CPUCAPACITY) the write-able interface still could make some sense.
E.g. by enabling SD_BALANCE_WAKE on the fly, I can force !want_affine wakees into slow path.
The question is, do people use the writable flags interface to tweak select_task_rq_fair() behavior in this regard?
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