I am hoping that we well get further cleanups, but art this point I'm not sure it is worth blocking it for 3.15 over that
On March 27, 2014 1:44:00 PM PDT, John Stultz <john.stu...@linaro.org> wrote: >On 03/17/2014 03:22 PM, Stefani Seibold wrote: >> This patch add the VDSO time support for the IA32 Emulation Layer. >> >> Due the nature of the kernel headers and the LP64 compiler where the >> size of a long and a pointer differs against a 32 bit compiler, there >> is some type hacking necessary for optimal performance. >> >> The vsyscall_gtod_data struture must be a rearranged to serve 32- and >> 64-bit code access at the same time: >> >> - The seqcount_t was replaced by an unsigned, this makes the >> vsyscall_gtod_data intedepend of kernel configuration and internal >functions. >> - All kernel internal structures are replaced by fix size elements >> which works for 32- and 64-bit access >> - The inner struct clock was removed to pack the whole struct. >> >> The "unsigned seq" would be handled by functions derivated from >seqcount_t. > >Sorry for being a bit late on the review here. I've been focused on >some >other things and figured I'd leave things to the x86 maintainers, since >it didn't touch any core timekeeping code. But Andy pinged me after >LSF-MM and so I'm trying to take a closer look. > >I know this has gone through tons of iterations, and I really am glad >for Stefani's persistence. Also I do realize its already in the tip >tree, so my thoughts here are probably too late to be worth much. > > >> Signed-off-by: Stefani Seibold <stef...@seibold.net> >> --- >> arch/x86/include/asm/vgtod.h | 71 >+++++++++++++++++++++------ >> arch/x86/include/asm/vvar.h | 5 ++ >> arch/x86/kernel/vsyscall_gtod.c | 34 ++++++++----- >> arch/x86/vdso/vclock_gettime.c | 91 >+++++++++++++++++++---------------- >> arch/x86/vdso/vdso32/vclock_gettime.c | 21 ++++++++ >> 5 files changed, 155 insertions(+), 67 deletions(-) > >My initial issue with this patch is it is doing quite a few things that >could have been split up a bit. There's a number of separate cleanups: >seqlock change, the read_hpet_counter() cleanup, the vsyscall_gtod_data >structure rework, and finally the gtod_long_t and VDSO32_64 changes. > >Its probably too late now, but in the future it might be good to try to >split these sorts of things up in smaller chunks. > >Overall, I don't see any obvious correctness issues with the code, so >it >looks ok to me, but I really worry the amount of open-coded logic and >the quirkiness of trying to make the vsyscall_gtod_data structure >usable >for both architectures at the same time really makes this code quite >fragile. Looking over this there were lots of "oh, that's broken.. >wait.. no.. actually that will work" moments. So I'm worried about the >maintenance burden in the future from it. > >Having separate structures that are filled by update_vsyscall might be >nice to avoid needing the open-coded bits, but that would require >basically making a copy of all the data in the structure each update, >so >that might not be worth the cost. > >So as long as the x86 folks are ok with being on the hook for it, I'll >not get in the way (most other arches have quirky/ugly implementations >for their vdso/vsyscall/fsyscall/etc, so why not join the club :). > >I did run this through my timekeeping test suite and on 64bit nothing >broke w/ either 32 or 64bit binaries, but I also don't have the glibc >changes to enable the 32bit vdso, so all that says is its not showing >any regressions for my existing setup. > >thanks >-john -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- 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/
