On Wed, 7 Oct 2015 20:33:56 -0400 Chris Metcalf <cmetcalf@xxxxxxxxxx> wrote: > On 10/5/2015 1:07 PM, Luiz Capitulino wrote: > > On Mon, 28 Sep 2015 11:17:20 -0400 > > Chris Metcalf <cmetcalf@xxxxxxxxxx> wrote: > > > >> The new "task_isolation_debug" flag simplifies debugging > >> of TASK_ISOLATION kernels when processes are running in > >> PR_TASK_ISOLATION_ENABLE mode. Such processes should get no > >> interrupts from the kernel, and if they do, when this boot flag is > >> specified a kernel stack dump on the console is generated. > >> > >> It's possible to use ftrace to simply detect whether a task_isolation > >> core has unexpectedly entered the kernel. But what this boot flag > >> does is allow the kernel to provide better diagnostics, e.g. by > >> reporting in the IPI-generating code what remote core and context > >> is preparing to deliver an interrupt to a task_isolation core. > >> > >> It may be worth considering other ways to generate useful debugging > >> output rather than console spew, but for now that is simple and direct. > > Honest question: does any of the task_isolation_debug() calls added > > by this patch take care of the case where vmstat_shepherd() may > > schedule vmstat_update() to run because a TASK_ISOLATION process is > > changing memory stats? > > The task_isolation_debug() calls don't "take care of" any cases - they are > really just there to generate console dumps when the kernel unexpectedly > interrupts a task_isolated task. > > The idea with vmstat is that before a task_isolated task returns to > userspace, it quiesces the vmstat thread (does a final sweep to collect > the stats and turns off the scheduled work item). As a result, the vmstat > shepherd won't run while the task is in userspace. When and if it returns > to the kernel, it will again sweep up the stats before returning to userspace. > > The usual shepherd mechanism on a housekeeping core might notice > that the task had entered the kernel and started changing stats, and > might then asynchronously restart the scheduled work, but it should be > quiesced again regardless on the way back out to userspace. OK, I've missed the (obvious) fact that the process has to enter the kernel to change stats. Thanks a lot for your explanation. > > If that's not taken care of yet, should we? I just don't know if we > > should call task_isolation_exception() or task_isolation_debug(). > > task_isolation_exception() is called when an exception (page fault or > similar) is generated synchronously by the running task and we want > to make sure to notify the task with a signal if it has set up STRICT mode > to indicate that it is not planning to enter the kernel. > > > In the case of the latter, wouldn't it be interesting to add it to > > __queue_work() then? > > Well, queuing remote work involves sending an IPI, and we already tag > both the SMP send side AND the client side IRQ side with a task_isolation_debug(), > so I expect in practice it would be detected. > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
