On Fri, 12 Aug 2016, Mathieu Poirier wrote: > > I am adding an interface to pass PMU specific configuration to the > driver. Since PMU drivers exist for different architecture and > drivers I am making the mechanism as generic as possible. It's a shame we are ending up with two "string configuration" ioctls. PERF_EVENT_IOC_SET_FILTER and this new one. Though I guess PERF_EVENT_IOC_SET_FILTER is not really set up to be used generically. > "@cfg" and "@cfg=option". The lexer will strip off the '@' and pass > "cfg" and "cfg=option" to the kernel. > > What gets sent down to the kernel is driver specific - it is up to the > PMU drivers to parse and validate what's given to them. But the core kernel is parsing "=" and "," in this case, so it's not entirely up to the PMU driver, right? Is there going to be a list of allowed keywords somewhere, under /sys or similar? >> .TP >> .BR PERF_EVENT_IOC_SET_DRV_CONFIGS " (since Linux 4.9)" >> Pass custom configuration paramaters to a PMU driver. >> >> The argument is a pointer to a NUL-termiated string of up to >> PAGE_SIZE in length. >> The string contains a list of comma-separated configuration options >> that will be parsed by the kernel. >> The kernel handles both singleton values as well as name/value pairs >> that are indicated with the '=' character. >> The size of the strings is limited internally to PERF_DRV_CONFIG_MAX >> (which is not visible to userspace). >> > Yes this is a very good description but in sharp contrast with what is > currently done for the ioctl() descriptors in this page. I shied away > from writing that much based on how slim the current descriptions were. Well that's because this interface is a lot more complex than some of the other ioctls which just take a simple integer (or no argument at all). The ftrace ioctl description could definitely use some expansion. > > some additional questions: can this ioctl be run at any time or should > > only be run while the event is quiet? Does the change in options take > > place immediately? > That is up to PMU drivers to decide - for CoreSight it is set only > once when trace sessions are created. Any changes from thereon will > be ignored. Then shouldn't this be set at perf_event_open() and not by an ioctl()? Vince -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
