kernel/linux.git/arch/arc/include/asm/atomic-llsc.h, branch linux-7.0.y

ARC: atomics: Add compiler barrier to atomic operations...

2023-08-16T00:27:26+00:00

... to avoid unwanted gcc optimizations SMP kernels fail to boot with commit 596ff4a09b89 ("cpumask: re-introduce constant-sized cpumask optimizations"). | | percpu: BUG: failure at mm/percpu.c:2981/pcpu_build_alloc_info()! | The write operation performed by the SCOND instruction in the atomic inline asm code is not properly passed to the compiler. The compiler cannot correctly optimize a nested loop that runs through the cpumask in the pcpu_build_alloc_info() function. Fix this by add a compiler barrier (memory clobber in inline asm). Apparently atomic ops used to have memory clobber implicitly via surrounding smp_mb(). However commit b64be6836993c431e ("ARC: atomics: implement relaxed variants") removed the smp_mb() for the relaxed variants, but failed to add the explicit compiler barrier. Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/135 Cc: # v6.3+ Fixes: b64be6836993c43 ("ARC: atomics: implement relaxed variants") Signed-off-by: Pavel Kozlov Signed-off-by: Vineet Gupta [vgupta: tweaked the changelog and added Fixes tag]

ARC: atomic: cleanup atomic-llsc definitions

2022-04-18T21:45:09+00:00

Remove redundant c_op macro argument. Only asm_op is needed to define atomic operations using llock/scond. Signed-off-by: Sergey Matyukevich Signed-off-by: Vineet Gupta

ARC: atomics: implement relaxed variants

2021-08-24T21:25:47+00:00

The current ARC fetch/return atomics provide fully ordered semantics only with 2 full barriers around the operation. Instead implement them as relaxed variants without any barriers and rely on generic code to generate the fully-ordered, acquire and release varaints by adding the appropriate full barriers. This helps elide some extra barriers in case of acquire/release/relaxed calls. bloat-o-meter for hsdk defconfig shows codegen improvements, although numbers below inflated due to unrelated inlining heuristic changes | bloat-o-meter vmlinux-643babe34fd7-non-relaxed vmlinux-45aa05cb44d7-relaxed | add/remove: 2/5 grow/shrink: 42/1222 up/down: 4158/-14312 (-10154) | Function old new delta | .. | sys_renameat 462 476 +14 | ip_mc_inc_group 424 436 +12 | do_read_cache_page 1882 1894 +12 | .. | refcount_dec_and_mutex_lock 254 250 -4 | refcount_dec_and_lock_irqsave 258 254 -4 | refcount_dec_and_lock 254 250 -4 | .. | tcp_v6_route_req 246 238 -8 | tcp_v4_destroy_sock 286 278 -8 | tcp_twsk_unique 352 344 -8 Link: https://lore.kernel.org/r/20180830144344.GW24142@hirez.programming.kicks-ass.net Suggested-by: Peter Zijlstra (Intel) Acked-by: Peter Zijlstra (Intel) Signed-off-by: Vineet Gupta

ARC: atomics: disintegrate header

2021-08-24T21:25:46+00:00

Non functional change, to ease future addition/removal Acked-by: Peter Zijlstra (Intel) Signed-off-by: Vineet Gupta