Le 27/11/2019 à 12:03, Arnd Bergmann a écrit :
On Thu, Nov 21, 2019 at 5:25 PM Christophe Leroy christophe.leroy@c-s.fr wrote:
Arnd Bergmann arnd@arndb.de a écrit :
On Wed, Nov 20, 2019 at 11:43 PM Ben Hutchings ben.hutchings@codethink.co.uk wrote:
On Fri, 2019-11-08 at 22:07 +0100, Arnd Bergmann wrote:
@@ -192,7 +190,7 @@ V_FUNCTION_BEGIN(__kernel_time) bl __get_datapage@local mr r9, r3 /* datapage ptr in r9 */
lwz r3,STAMP_XTIME+TSPEC_TV_SEC(r9)
lwz r3,STAMP_XTIME_SEC+LOWPART(r9)"LOWPART" should be "LOPART".
Thanks, fixed both instances in a patch on top now. I considered folding it into the original patch, but as it's close to the merge window I'd rather not rebase it, and this way I also give you credit for finding the bug.
Take care, might conflict with https://github.com/linuxppc/linux/commit/5e381d727fe8834ca5a126f510194a7a4ac...
Sorry for my late reply. I see this commit and no other variant of it has made it into linux-next by now, so I assume this is not getting sent for v5.5 and it's not stopping me from sending my own pull request.
Please let me know if I missed something and this will cause problems.
On a related note: are you still working on the generic lib/vdso support for powerpc? Without that, future libc implementations that use 64-bit time_t will have to use the slow clock_gettime64 syscall instead of the vdso, which has a significant performance impact.
I have left this generic lib/vdso subject aside for the moment, because performance is disappointing and its architecture doesn't real fit with powerpc ABI.
From a performance point of view, it is manipulating 64 bits vars where is could use 32 bits vars. Of course I understand that y2038 will anyway force the use of 64 bits for seconds, but at the time being powerpc32 VDSO is using 32 bits vars for both secs and ns, it make the difference. Also, the generic VDSO is playing too much with data on stacks and associated memory read/write/copies, which kills performance on RISC processors like powerpc. Inlining do_hres() for instance significantly improves that as it allow handling the 'struct __kernel_timespec ts' on registers instead of using stack.
Regarding powerpc ABI, the issue is that errors shall be reported by setting the SO bit in CR register, and this cannot be done in C. This means: - The VDSO entry point must be in ASM and the generic VDSO C function must be called from there, it cannot be the VDSO entry point. - The VDSO fallback (ie the system call) cannot be done from the generic VDSO C function, it must be called from the ASM as well.
Last point/question, what's the point in using 64 bits for nanoseconds on 32 bits arches ?
Christophe