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05 April 2024, 19:05:47 UTC
Revision e78fdfef84be13a5c2b8276e12203cdf24778596 authored by Vineet Gupta on 14 July 2015, 14:20:18 UTC, committed by Vineet Gupta on 04 August 2015, 03:56:34 UTC 
ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff
 
This is to workaround the llock/scond livelock

HS38x4 could get into a LLOCK/SCOND livelock in case of multiple overlapping
coherency transactions in the SCU. The exclusive line state keeps rotating
among contenting cores leading to a never ending cycle. So break the cycle
by deferring the retry of failed exclusive access (SCOND). The actual delay
needed is function of number of contending cores as well as the unrelated
coherency traffic from other cores. To keep the code simple, start off with
small delay of 1 which would suffice most cases and in case of contention
double the delay. Eventually the delay is sufficient such that the coherency
pipeline is drained, thus a subsequent exclusive access would succeed.

Link: http://lkml.kernel.org/r/1438612568-28265-1-git-send-email-vgupta@synopsys.com
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
1 parent 69cbe63
History
Tip revision: e78fdfef84be13a5c2b8276e12203cdf24778596 authored by Vineet Gupta on 14 July 2015, 14:20:18 UTC
ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff
Tip revision: e78fdfe
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