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a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=yJojWOMRYYMA:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=JfrnYn6hAAAA:8 a=vggBfdFIAAAA:8 a=yPCof4ZbAAAA:8 a=L6dDZDBz5GL0lWFFP4gA:9 a=a-qgeE7W1pNrGK8U0ZQC:22 a=1CNFftbPRP8L7MoqJWF3:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA4MDE2NSBTYWx0ZWRfX6ZP69U/HsOoN HbDNWgA+VieI3w2dav/8KzUWeQezFqruLW1qb+1t4nHFvCZNjhP+kafVDcoRYXFIG0TOIzG4Y2s bA8q6Xyk7pVyG5r5e4iYubA5mIJCILLHchskOpoSxaNZbs44dqrfXiS5TPYGIOilxEa2j3CUGat AxrldHUJIwXfrxm70q+8UBBZjGLBUeqnouJjbYruCDRzL062feyosQMTyam/umOzZuTfYPLk9H5 Y730EBCuelNRfVX9c8zt0wlabXKoNV97vtNfzBqmaPOl+hnrMG/vZsnaEqaxBGR0WfK6SuklwtA 6P0FF8QGiPsLwNk57nPMXBlo6bkVO05PVtpr1EI83/0hwFSn6H3cFOdkxjAmDhVJy5UI9yJPcCN A/OJvuK5 X-Proofpoint-GUID: ndoTVGKgoqsw9b7dmSTAx7sbyMq54NGk X-Proofpoint-ORIG-GUID: ndoTVGKgoqsw9b7dmSTAx7sbyMq54NGk 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 additional parameter allows for the timeout check. The waiting is done via the usual cpu_relax() spin-wait around the condition variable with periodic evaluation of the time-check. The number of times we spin is defined by SMP_TIMEOUT_SPIN_COUNT (chosen to be 200 by default) which, assuming each cpu_relax() iteration takes around 20-30 cycles (measured on a variety of x86 platforms), amounts to around 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 | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index d4f581c1e21d..8483e139954f 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -273,6 +273,41 @@ do { \ }) #endif =20 +#ifndef SMP_TIMEOUT_SPIN_COUNT +#define SMP_TIMEOUT_SPIN_COUNT 200 +#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_SPIN_COUNT; \ + \ + for (;;) { \ + VAL =3D READ_ONCE(*__PTR); \ + if (cond_expr) \ + break; \ + cpu_relax(); \ + if (++__n < __spin) \ + continue; \ + if (time_check_expr) \ + 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