Messages in this thread Patch in this message | | | Date | Wed, 31 May 2017 11:00:21 +0200 | From | Richard Cochran <> | Subject | Re: [patch 05/26] posix-clocks: Remove interval timer facility and mmap/fasync callbacks |
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On Tue, May 30, 2017 at 11:15:38PM +0200, Thomas Gleixner wrote: > The only user of this facility is ptp_clock, which does not implement any of > those functions. > > Remove them to prevent accidental users. Especially the interval timer > interfaces are now more or less impossible to implement because the > necessary infrastructure has been confined to the core code. Aside of that > it's really complex to make these callbacks implemented according to spec > as the alarm timer implementation demonstrates. If at all then a nanosleep > callback might be a reasonable extension. For now keep just what ptp_clock > needs. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Richard Cochran <richardcochran@gmail.com>
For the record, recently someone did try to implement this interface for the i210 card. Although there were issues in the implementation, still I was curious enough to test the performance.
https://www.mail-archive.com/linuxptp-devel@lists.sourceforge.net/msg01738.html
The result confirmed my expectation that using the normal system clock sychronized to the PHC using the phc2sys utility yields better performance than the direct timer_settime() implementation.
The nanosleep() idea might be worthwhile, but only for devices with directly mapped registers (like in some SoCs) and not for the common PCIe devices. In any case, I am happy to see the timer interface removed, as it is basically useless and gives people false impressions.
Could you please include this documentation fix, too?
Thanks, Richard
---8<--- diff --git a/Documentation/ptp/ptp.txt b/Documentation/ptp/ptp.txt index ae8fef8..11e904e 100644 --- a/Documentation/ptp/ptp.txt +++ b/Documentation/ptp/ptp.txt @@ -18,7 +18,6 @@ - Adjust clock frequency + Ancillary clock features - - One short or periodic alarms, with signal delivery to user program - Time stamp external events - Period output signals configurable from user space - Synchronization of the Linux system time via the PPS subsystem @@ -48,9 +47,7 @@ User space programs may control the clock using standardized ioctls. A program may query, enable, configure, and disable the ancillary clock features. User space can receive time stamped - events via blocking read() and poll(). One shot and periodic - signals may be configured via the POSIX timer_settime() system - call. + events via blocking read() and poll(). ** Writing clock drivers
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