On 08/10/2014 09:19 PM, Benjamin Herrenschmidt wrote: > On Wed, 2014-07-30 at 00:31 -0700, tip-bot for John Stultz wrote: >> Commit-ID: 953dec21aed4038464fec02f96a2f1b8701a5bce >> Gitweb: >> http://git.kernel.org/tip/953dec21aed4038464fec02f96a2f1b8701a5bce >> Author: John Stultz <john.stu...@linaro.org> >> AuthorDate: Fri, 25 Jul 2014 21:37:19 -0700 >> Committer: Thomas Gleixner <t...@linutronix.de> >> CommitDate: Wed, 30 Jul 2014 09:26:25 +0200 >> >> timekeeping: Fixup typo in update_vsyscall_old definition >> >> In commit 4a0e637738f0 ("clocksource: Get rid of cycle_last"), >> currently in the -tip tree, there was a small typo where cycles_t >> was used intstead of cycle_t. This broke ppc64 builds. > There's another bug in there... You fix timespec vs. timespec64 for the > first argument of update_vsyscall_old but not the second one ... > (wall_to_monotonic). > > Also, in e2dff1ec0 you claim this is "minor", you seem to forget that > arch/powerpc also deals with 32-bit kernels which use the same time > keeping code, so we have a pretty serious regressions here... Yikes. My apologies. I had missed that issue and had forgotten ppc32 has the vsyscall support as well.
Thanks for pointing it out. I'll send a fix here shortly (though I only have the ppc64le toolchain handy, so forgive me if its not quite right). > BTW. Is there some documentation you can point me to to figure out what > replace that "_OLD" stuff so we can update to whatever is "new" ? So there's not exactly documentation, but the idea is rather then doing: nsecs + (mult*(now - cycle_last) >>shift); We're preserving the sub-nanosecond precision, and doing: (shifted_nsecs + mult*(now-cycle_last)) >> shift This avoids the rounding up 1ns every tick, which we did to avoid errors from truncating the precision. I think the hard part for ppc, is if I recall, ppc's vsyscall exports the xsec unit, which less granular then nanoseconds, so it had its own version of the same precision truncation issues. I recall Paul working on that, and I thought his solution was to reduce the multiplier by one so the inter-tick time was slightly slower, then the tick update would catch up causing a slight stair-step, which isn't ideal but is better then the inconsistencies that came out of not-handling the precision properly. That said, skimming the ppc code, I don't see that logic right off, and have a fuzzy memory that maybe that solution was RHEL5 specific or something like that. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
