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a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=vUbySO9Y5rIA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=oAwlwhGTAOkQKmTHlAcA:9 X-Proofpoint-GUID: LPEtVpBKxWKVPEv0huXfbRdRRMPcR_XW X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTA5MDA2NCBTYWx0ZWRfX+HeG1ZJfSJ9n dd+D8GyEZBHxC35N96D14ynhlzRqjwuXpAs944rUycrgYybh12UG+Q6KyIp3acwcUmjjpKaMeFU 2vgmJcIEDsK+2dPSJbp74BRXiiA/MnaF9ENghWxRFP2u9Nfg1fDJJbHcAQ+jLBXyjgpR5eKconW FXFu3TWI4BeTA4Blve7+8+dChYhaZV34wWOwl393TbDziSBay/29unie4HBIoV7E8U1KhDTeXqa 9ucyFMXxt7I2U6XzqLujGtSwCJTUnishsMT/a4fFlBpcqZq/2yiRpZN9Z/abYX7WBnpuiiJjU8m QluylM7X4Aw5aLBsNrwSol0Pw8y2gHvepXYmRDlaq9kvAilyhBOofml02pRUzfsjLhTT1dmpG+H 8KDt7aqb/KCL3OlfIgV16l2PoBkwXIHoYJG0th7JysHaHmHILWgErqycIKLMpOlf2m7rNFRZiOb 1OC+A6EeuZwfXb7gYAQ== X-Proofpoint-ORIG-GUID: LPEtVpBKxWKVPEv0huXfbRdRRMPcR_XW Will Deacon writes: > On Sun, Dec 14, 2025 at 08:49:11PM -0800, Ankur Arora wrote: >> +#define __CMPWAIT_CASE(w, sfx, sz) \ >> +static inline void __cmpwait_case_##sz(volatile void *ptr, \ >> + unsigned long val, \ >> + s64 timeout_ns) \ >> +{ \ >> + unsigned long tmp; \ >> + \ >> + if (!alternative_has_cap_unlikely(ARM64_HAS_WFXT) || timeout_ns <= 0) { \ >> + asm volatile( \ >> + " sevl\n" \ >> + " wfe\n" \ >> + " ldxr" #sfx "\t%" #w "[tmp], %[v]\n" \ >> + " eor %" #w "[tmp], %" #w "[tmp], %" #w "[val]\n" \ >> + " cbnz %" #w "[tmp], 1f\n" \ >> + " wfe\n" \ >> + "1:" \ >> + : [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr) \ >> + : [val] "r" (val)); \ >> + } else { \ >> + u64 ecycles = arch_timer_read_counter() + \ >> + NSECS_TO_CYCLES(timeout_ns); \ >> + asm volatile( \ >> + " sevl\n" \ >> + " wfe\n" \ >> + " ldxr" #sfx "\t%" #w "[tmp], %[v]\n" \ >> + " eor %" #w "[tmp], %" #w "[tmp], %" #w "[val]\n" \ >> + " cbnz %" #w "[tmp], 2f\n" \ >> + " msr s0_3_c1_c0_0, %[ecycles]\n" \ >> + "2:" \ >> + : [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr) \ >> + : [val] "r" (val), [ecycles] "r" (ecycles)); \ >> + } \ > > Why not have a separate helper for the WFXT version and avoid the runtime > check on timeout_ns? My main reason for keeping them together was that a separate helper needed duplication of a lot of the __CMPWAIT_CASE and __CMPWAIT_GEN stuff. Relooking at it, I think we could get by without duplicating the __CMPWAIT_GEN (the WFE helper just needs to take an unused timeout_ns paramter). But, it seems overkill to get rid of the unnecessary check on timeout_ns (which AFAICT should be well predicted) and the duplicate static branch. -- ankur