On Tue, 3 Jul 2018 at 04:57, Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx> wrote: > > On Tue, Jul 03, 2018 at 01:03:48PM +0300, Alexander Shishkin wrote: > > On Mon, Jul 02, 2018 at 04:33:29PM -0600, Mathieu Poirier wrote: > > > +/* > > > + * PMU driver configuration works the same way as filter management above, > > > + * but without the need to deal with memory mapping. Driver configuration > > > + * arrives through the SET_DRV_CONFIG ioctl() where it is validated and applied > > > + * to the event. When the PMU is ready it calls perf_event_drv_config_sync() to > > > + * bring the configuration information within reach of the PMU. > > > > Wait a second. The reason why we dance around with the generations of filters > > is the locking order of ctx::mutex vs mmap_sem. In an mmap path, where we're > > notified about mapping changes, we're called under the latter, and we'd need > > to grab the former to update the event configuration. In your case, the > > update comes in via perf_ioctl(), where we're already holding the ctx::mutex, > > so you can just kick the PMU right there, via an event_function_call() or > > perf_event_stop(restart=1). In the latter case, your pmu::start() would just > > grab the new configuration. Should also be about 90% less code. :) > > Also, since it affects the AUX buffer configuration, it is probably a one > time ioctl command that you issue before you mmap the buffer. If that's > the case, you don't even have to worry about stopping the event, as it > shouldn't be running, because without the buffer perf_aux_output_begin() > should fail and so should the pmu::add() iirc. > The idea behind the current approach was to make the SET_DRV_CONFIG ioctl() usable by other drivers where multiple ioctl() calls could be performed while a session in ongoing. I also opted to introduce a _sync() function to let the PMU refresh its configuration at the time of its own choosing rather than having to interrupt the session. But all I need for coresight is to have available the sink information and PMU configuration (in an upcoming patchset) by the time setup_aux() is called. You are correct, this is a one time configuration and since the event isn't running there is no need for locking - I should be able to access the PMU when the ioctl is called. If you are fine with this bare-bone scenario and don't care much about usability in different situation, I'll do a respin with minimal functionality that cover my needs. Thanks for the review, Mathieu > Regards, > -- > Alex -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
