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Re: [PATCHv2 2/4] Cleanup hp-timing defines
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>, 'GNU C Library' <libc-alpha at sourceware dot org>
- Cc: nd <nd at arm dot com>
- Date: Thu, 7 Feb 2019 14:00:35 +0000
- Subject: Re: [PATCHv2 2/4] Cleanup hp-timing defines
> I think since we are touching it, we should aim to clean up the hp-timing
> usage not only for benchtests. Current internal hp-timing usage should be
> aimed for time profiling and we can clean up its internal usage since:
Yes it makes sense to remove all internal use of hp-timing except for
benchmarking and rtld profiling.
> - clock_gettime, clock_settime, clock_getres, clock_nanosleep support
> for CLOCK_THREAD_CPUTIME_ID and CLOCK_PROCESS_CPUTIME_ID are not used
> neither on Linux nor on Hurd. It also means that assuming clock_*
> syscall always support such clock ids, pthread_clock_gettime.c
> and pthread_clock_settime.c are also unused. Which also leads to
> note that _dl_cpuclock_offset is also set and not used for none of
> the hp-timing architectures.
Getting rid of the badly hacked emulation of clock_gettime etc allows for a
lot of code to be removed. It's clearly not needed for Linux, but what about Hurd?
> - same for sysconf, where assuming CLOCK_THREAD_CPUTIME_ID and
> CLOCK_PROCESS_CPUTIME_ID support we can get rid of hp-timing usage.
> - the remaining 3 usages of hp-timing for some sort of randomness
> at resolv/res_mkquery.c, resolv/res_send.c, and sysdeps/posix/tempname.c
> could be replaced to clock_gettime (CLOCK_MONOTONIC) instead.
> If randomness is really required I think we should refactor to
> use a better source (getrandom/getentropy).
In all cases we don't need true randomness, just a fast random number to
reduce collisions. It seems best to abstract these cases into an internal interface.
> Also, I understand why you refactor removes ld.so profiling for alpha
> (since it is hp-timing support is sketchy at least and sit simplifies
> the benchtests inclusion of generic implementation). However I think
> we can still maintain it supports by enable the architecture hp-timing
> support only for rtld.
Yes that's feasible.
> Based on that I created a branch  with the above refactor along with
> your suggestion to add a generic hp-timing based on clock_gettime. What
> do you think?
It looks like a good cleanup. Are you planning to post patches for this, either
subsuming my patches or on top of my cleanup?