----- On Jun 14, 2018, at 10:41 AM, Florian Weimer fwei...@redhat.com wrote:
> On 06/14/2018 04:36 PM, Mathieu Desnoyers wrote: >> ----- On Jun 14, 2018, at 10:00 AM, Florian Weimer fwei...@redhat.com wrote: >> >>> On 06/14/2018 03:49 PM, Pavel Machek wrote: >>>> Hi! >>>> >>>>>>> - rseq_preempt(): on preemption, the scheduler sets the >>>>>>> TIF_NOTIFY_RESUME thread >>>>>>> flag, so rseq_handle_notify_resume() can check whether it's in a >>>>>>> rseq critical >>>>>>> section when returning to user-space, >>>>>>> - rseq_signal_deliver(): on signal delivery, >>>>>>> rseq_handle_notify_resume() checks >>>>>>> whether it's in a rseq critical section, >>>>>>> - rseq_migrate: on migration, the scheduler sets TIF_NOTIFY_RESUME as >>>>>>> well, >>>>>> >>>>>> Yes, this is not likely to be noticeable. >>>>>> >>>>>> But the proposal wanted to add a syscall to thread creation, right? >>>>>> And I believe that may be noticeable. >>>>> >>>>> Fair point! Do we have a standard benchmark that would stress this ? >>>> >>>> Web server performance benchmarks basically test clone() performance >>>> in many cases. >>> >>> Isn't that fork? I expect that the rseq arena is inherited on fork and >>> fork-type clone, otherwise it's going to be painful. >> >> On fork or clone creating a new process, the rseq tls area is inherited >> from the thread that does the fork syscall. >> >> On creation of a new thread with clone, there is no such inheritance. > > Makes sense. So fork-based (web) servers will not be impacted by the > additional system call, and thread-based servers likely use a thread > pool anyway. I'm not really concerned about the additional system call > here. Just for the sake of completeness, there is (of course) no inheritance on exec(). So glibc would also have to register the rseq TLS in its constructors. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
