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wEDouLH+9lP10XgL3jQCclXJGox3pYMLaIJHF1/b+DNNJjBD8PeSpWIcYoj+/LJ4uy2NGtz0zZR J6hGMqo5Fr0sTXIagIeMq9XEASDWIg7bEvEiM0e2xttyOl3dne9OMASZuLxFI5kM7UwXT2ZuWU3 +kULxYEdpZGIVPfGi0F0FUGDxZ5/qfmtAInprmrnwOJoLEpVF8jB0sK6NlFRWhDuMgo+Zxacbiy 1Xo4XO3YhFPp3SSeDo2I9koHNSELRv90XFYyvP7hhZTUVnVHBGWObR6SwzkTnatTCEDYKmmVNpH K2HIovPQzAHnuuRnpmudnCmFLnDoTg== X-Authority-Analysis: v=2.4 cv=E7TAZKdl c=1 sm=1 tr=0 ts=68f1df2e cx=c_pps a=OOZaFjgC48PWsiFpTAqLcw==:117 a=OOZaFjgC48PWsiFpTAqLcw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=x6icFKpwvdMA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=JfrnYn6hAAAA:8 a=vggBfdFIAAAA:8 a=yPCof4ZbAAAA:8 a=tAfxz9XjlOImCDDYAN4A:9 a=a-qgeE7W1pNrGK8U0ZQC:22 a=1CNFftbPRP8L7MoqJWF3:22 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-GUID: 87NYcqJfBr1yXWvTuZIhTAh3kDkx3tlB Content-Type: text/plain; charset="utf-8" Add smp_cond_load_relaxed_timeout(), which extends smp_cond_load_relaxed() to allow waiting for a duration. The waiting loop uses cpu_poll_relax() to wait on the condition variable with a periodic evaluation of a time-check. cpu_poll_relax() unless overridden by the arch code, amounts to a cpu_relax(). The number of times we spin is defined by SMP_TIMEOUT_POLL_COUNT (chosen to be 200 by default) which, assuming each cpu_poll_relax() iteration takes around 20-30 cycles (measured on a variety of x86 platforms), for a total of ~4000-6000 cycles. Cc: Arnd Bergmann Cc: Will Deacon Cc: Catalin Marinas Cc: Peter Zijlstra Cc: linux-arch@vger.kernel.org Reviewed-by: Catalin Marinas Reviewed-by: Haris Okanovic Tested-by: Haris Okanovic Signed-off-by: Ankur Arora --- include/asm-generic/barrier.h | 41 +++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index d4f581c1e21d..0063b46ec065 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -273,6 +273,47 @@ do { \ }) #endif =20 +#ifndef SMP_TIMEOUT_POLL_COUNT +#define SMP_TIMEOUT_POLL_COUNT 200 +#endif + +#ifndef cpu_poll_relax +#define cpu_poll_relax(ptr, val) cpu_relax() +#endif + +/** + * smp_cond_load_relaxed_timeout() - (Spin) wait for cond with no ordering + * guarantees until a timeout expires. + * @ptr: pointer to the variable to wait on + * @cond: boolean expression to wait for + * @time_check_expr: expression to decide when to bail out + * + * Equivalent to using READ_ONCE() on the condition variable. + */ +#ifndef smp_cond_load_relaxed_timeout +#define smp_cond_load_relaxed_timeout(ptr, cond_expr, time_check_expr) \ +({ \ + typeof(ptr) __PTR =3D (ptr); \ + __unqual_scalar_typeof(*ptr) VAL; \ + u32 __n =3D 0, __spin =3D SMP_TIMEOUT_POLL_COUNT; \ + \ + for (;;) { \ + VAL =3D READ_ONCE(*__PTR); \ + if (cond_expr) \ + break; \ + cpu_poll_relax(__PTR, VAL); \ + if (++__n < __spin) \ + continue; \ + if (time_check_expr) { \ + VAL =3D READ_ONCE(*__PTR); \ + break; \ + } \ + __n =3D 0; \ + } \ + (typeof(*ptr))VAL; \ +}) +#endif + /* * pmem_wmb() ensures that all stores for which the modification * are written to persistent storage by preceding instructions have --=20 2.43.5