On 07/24/2013 04:01 PM, Rakib Mullick wrote: > On Wed, Jul 24, 2013 at 9:26 AM, Michael Wang > <wang...@linux.vnet.ibm.com> wrote: >> Hi, Rakib >> >> On 07/24/2013 01:42 AM, Rakib Mullick wrote: >>> Currently, update_top_cache_domain() is called whenever schedule domain is >>> built or destroyed. But, the following >>> callpath shows that they're at the same callpath and can be avoided >>> update_top_cache_domain() while destroying schedule >>> domain and update only at the times of building schedule domains. >>> >>> partition_sched_domains() >>> detach_destroy_domain() >>> cpu_attach_domain() >>> update_top_cache_domain() >> >> IMHO, cpu_attach_domain() and update_top_cache_domain() should be >> paired, below patch will open a window which 'rq->sd == NULL' while >> 'sd_llc != NULL', isn't it? >> >> I don't think we have the promise that before we rebuild the stuff >> correctly, no one will utilize 'sd_llc'... >> > I never said it. My point is different. partition_sched_domain works as - > > - destroying existing schedule domain (if previous domain and new > domain aren't same) > - building new partition > > while doing the first it needs to detach all the cpus on that domain. > By detaching what it does, > it fall backs to it's root default domain. In this context (which i've > proposed to skip), by means > of updating top cache domain it takes the highest flag domain to setup > it's sd_llc_id or cpu itself. > > Whatever done above gets overwritten (updating top cache domain), > while building new partition. > Then, why we did that before? Hope you understand my point.
I think you missed this in PeterZ's suggestion: - cpu_attach_domain(NULL, &def_root_domain, i); With this change, it will be safe since you will still get an un-freed sd, although it's an old one. But your patch will run the risk to get a freed sd, since you make 'sd_llc' wrong for a period of time (between destroy and rebuild) IMO. I guess I get you point, you are trying to save one time update since you think this will be done twice, but actually the result of this two time update was different, it's not redo and it's in order to sync 'sd_llc' with 'rq->sd'. Regards, Michael Wang > > Thanks, > Rakib. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
