----- On Jul 24, 2016, at 2:01 PM, Dave Watson davejwatson@xxxxxx wrote:
>>> +static inline __attribute__((always_inline))
>>> +bool rseq_finish(struct rseq_lock *rlock,
>>> + intptr_t *p, intptr_t to_write,
>>> + struct rseq_state start_value)
>
>>> This ABI looks like it will work fine for our use case. I don't think it
>>> has been mentioned yet, but we may still need multiple asm blocks
>>> for differing numbers of writes. For example, an array-based freelist push:
>
>>> void push(void *obj) {
>>> if (index < maxlen) {
>>> freelist[index++] = obj;
>>> }
>>> }
>
>>> would be more efficiently implemented with a two-write rseq_finish:
>
>>> rseq_finish2(&freelist[index], obj, // first write
>>> &index, index + 1, // second write
>>> ...);
>
>> Would pairing one rseq_start with two rseq_finish do the trick
>> there ?
>
> Yes, two rseq_finish works, as long as the extra rseq management overhead
> is not substantial.
I've added a commit implementing rseq_finish2() in my rseq volatile
dev branch. You can fetch it at:
https://github.com/compudj/linux-percpu-dev/tree/rseq-fallback
I also have a separate test and benchmark tree in addition to the
kernel selftests here:
https://github.com/compudj/rseq-test
I named the first write a "speculative" write, and the second write
the "final" write.
Would you like to extend the test cases to cover your intended use-case ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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