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Groups > comp.lang.c++ > #120767
| From | jseigh <jseigh_es00@xemaps.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: smrproxy v2 |
| Date | 2024-10-28 21:17 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <vfpd43$186t4$1@dont-email.me> (permalink) |
| References | (9 earlier) <vfmf21$kavl$1@dont-email.me> <vfmm9a$lob3$1@dont-email.me> <vfn2di$r8ca$1@dont-email.me> <vfntgb$vete$1@dont-email.me> <vfp1c3$16d9f$1@dont-email.me> |
On 10/28/24 17:57, Chris M. Thomasson wrote:
> On 10/28/2024 4:45 AM, jseigh wrote:
>> On 10/28/24 00:02, Chris M. Thomasson wrote:
>>> On 10/27/2024 5:35 PM, jseigh wrote:
>>>> On 10/27/24 18:32, Chris M. Thomasson wrote:
>>
>>>>
>>>> The membar version? That's a store/load membar so it is expensive.
>>>
>>> I was wondering in your c++ version if you had to use any seq_cst
>>> barriers. I think acquire/release should be good enough. Now, when I
>>> say C++, I mean pure C++, no calls to FlushProcessWriteBuffers and
>>> things like that.
>>>
>>> I take it that your pure C++ version has no atomic RMW, right? Just
>>> loads and stores?
>>
>> While a lock action has acquire memory order semantics, if the
>> implementation has internal stores, you have to those stores
>> are complete before any access from the critical section.
>> So you may need a store/load memory barrier.
>
> Wrt acquiring a lock the only class of mutex logic that comes to mind
> that requires an explicit storeload style membar is Petersons, and some
> others along those lines, so to speak. This is for the store and load
> version. Now, RMW on x86 basically implies a StoreLoad wrt the LOCK
> prefix, XCHG aside for it has an implied LOCK prefix. For instance the
> original SMR algo requires a storeload as is on x86/x64. MFENCE or LOCK
> prefix.
>
> Fwiw, my experimental pure C++ proxy works fine with XADD, or atomic
> fetch-add. It needs an explicit membars (no #StoreLoad) on SPARC in RMO
> mode. On x86, the LOCK prefix handles that wrt the RMW's themselves.
> This is a lot different than using stores and loads. The original SMR
> and Peterson's algo needs that "store followed by a load to a different
> location" action to hold true, aka, storeload...
>
> Now, I don't think that a data-dependant load can act like a storeload.
> I thought that they act sort of like an acquire, aka #LoadStore |
> #LoadLoad wrt SPARC. SPARC in RMO mode honors data-dependencies. Now,
> the DEC Alpha is a different story... ;^)
>
fwiw, here's the lock and unlock logic from smrproxy rewrite
inline void lock()
{
epoch_t _epoch = shadow_epoch.load(std::memory_order_relaxed);
_ref_epoch.store(_epoch, std::memory_order_relaxed);
std::atomic_signal_fence(std::memory_order_acquire);
}
inline void unlock()
{
_ref_epoch.store(0, std::memory_order_release);
}
epoch_t is interesting. It's uint64_t but handles wrapped
compares, ie. for an epoch_t x1 and uint64_t n
x1 < (x1 + n)
for any value of x1 and any value of n from 0 to 2**63;
eg.
0xfffffffffffffff0 < 0x0000000000000001
The rewrite is almost complete except for some thread_local
stuff. I think I might break off there. Most of the
additional work is writing the test code. I'm considering
rewriting it in Rust.
Joe Seigh
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smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-17 08:10 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-17 13:10 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-17 17:08 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-17 16:40 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-17 17:16 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-17 17:24 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-18 08:07 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-25 15:00 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-25 18:56 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 12:33 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-27 18:29 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 15:32 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-27 20:35 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 21:02 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-28 07:45 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-28 14:57 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-28 15:09 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-28 21:17 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-28 21:35 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-29 07:23 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 14:51 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-28 21:38 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-29 07:27 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 14:56 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-30 12:36 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-01 12:20 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-28 21:41 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 15:05 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-30 12:39 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-03 21:14 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-04 07:46 -0500
Re: smrproxy v2 Muttley@DastartdlyHQ.org - 2024-11-04 14:09 +0000
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-04 12:42 -0800
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-09 13:51 -0800
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-12-12 00:43 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-12-12 07:29 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-12-12 13:55 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-12-12 19:48 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-12-25 20:36 -0800
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 21:08 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 21:09 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 21:13 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-28 22:02 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 23:40 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 23:42 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 23:53 -0700
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-29 23:54 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-10-30 12:43 -0400
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-02 13:50 -0700
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-21 15:17 -0500
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-23 11:10 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-23 13:31 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-23 17:12 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-23 17:46 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-24 15:14 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-24 15:19 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-24 19:09 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-24 16:37 -0800
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-24 16:48 -0800
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-24 16:47 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-25 06:31 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-25 14:12 -0800
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-11-27 10:29 -0500
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-12-09 13:34 -0500
Re: smrproxy v2 jseigh <jseigh_es00@xemaps.com> - 2024-12-11 07:13 -0500
Re: smrproxy v2 "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-12-11 16:22 -0800
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