On Mon, Dec 6, 2010 at 7:58 AM, Nikos Chantziaras <rea...@arcor.de> wrote: > On 12/06/2010 04:33 PM, Stroller wrote: >> >> On 27/11/2010, at 10:22pm, Nikos Chantziaras wrote: >>>> >>>> ... >>>> Does using the ck-sources kernel reduce the necessity to use ionice? >>> >>> To some degree, yes. >> >> Tried this late last week. You chose your words perfectly - there is only >> some degree of improvement. >> >> The machine seems much snappier if I return to an interactive session >> after leaving it idle for some time, but during DVD rips it is still >> unresponsive for tens of seconds at a time. It seems like maybe it responds >> quicker than mainline sources, but it's still so slow that it's both >> unusable and hard to be sure whether that's the case. >> >> Will try cgroups this week, perhaps. > > cgroups will not help with that either. I bet the problem is that the > kernel doesn't care about what kind of data it is caching. I came across > this on LKML, but no one was interested in a solution. > > The problem is that the kernel caches all data. Ripping a DVD will consume > 4GB cache, and all other data will be thrown out. Throwing that all out > again after the rip has finished is an awful lot of I/O load. The smart > thing to do would be for the kernel to not cache such stuff (DVD rips, big > video files, etc.) But it does.
I forgot to ask Stroller if he's looked at top while these delays happen. If the issue is writing to disk from cached memory then what I saw when that was occurring (and during the times my system was unresponsive) was very low CPU usage while having very high wait percentages. In my 6 core/12 thread top display I'd see 2 or 3 CPUs involved in the wait (writing data out but delayed by responses from the disk driver I suppose) while the other CPUs were essentially idle, presumably because they couldn't get to disk for whatever they needed. - Mark
