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Re: About Distributed Reader-Writer Mutex by Dmitry Vyukov

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Patricia Shanahan wrote:
> The text explanation on the referenced web page says 'No additional
> synchronization between writers is required, writers acquire the mutexes
> in the same order (from 0 to P-1), so ownership over mutex 0 basically
> determines who is the "current" writer (all other potential writers are
> parked on mutex 0).'



You are absolutly right.


Thank you,
Amine Moulay Ramdane.


"aminer" <aminer@videotron.ca> wrote in message 
news:k1bo6h$m94$1@dont-email.me...
>
> Hello,
>
> Dmitry Vyukov  wrote this:
>
> "In order to a reader-writer mutex to scale reader's time under mutex must
> be significant, on the order of, let's say, 10'000 cycles. And the more 
> hardware
> threads you have the longer the time must be. Otherwise, inter-reader 
> synchronization
> overheads dominate, and the system does not scale."
>
> Read here:
>
> http://www.1024cores.net/home/lock-free-algorithms/reader-writer-problem/distributed-reader-writer-mutex
>
>
> I have done some tests with my light weight MREW and my lockfree mpmc
> fifo queue and what i think is that the CAS is generating a lot of 
> contention this is is why
> my rwlock is not scaling.
>
> What you are doing Dmitry Vyukovin in your distributed rwlock is lowering 
> the contention
> using the same method as lock striping it is why it is scaling, but there 
> is still a possibility
> of contention that can cause a problem to the scalability if you are not 
> setting the number
> of rwlocks inside your distributed rwlock correctly.
>
>
> other than that:
>
> I have looked at the Distributed Reader-Writer Mutex by Dmitry Vyukov, 
> look
> at it here:"
>
> http://www.1024cores.net/home/lock-free-algorithms/reader-writer-problem/distributed-reader-writer-mutex
>
>
> and i think there is a problem with this method,  cause look at the write
> lock function:
>
>
> int         distr_rw_mutex_wrlock(distr_rw_mutex_t* mtx)
> {
>    int                     i;
>    for (i = 0; i != mtx->proc_count; i += 1)
>        pthread_rwlock_wrlock(&mtx->cell[i].mtx);
>    return 0;
> }
>
>
> What is wrong with it ? suppose two or more writers want to lock this
> distributed rwlock there is a possibility of a deadlock.
>
> So i think you have to use a critical section around the for loop to be 
> able
> to lock all the rwlocks atomically to avoid the deadlock problem..
>
>
>
>
> Thank you,
> Amine Moulay Ramdane.
>
>
>
>
>
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About Distributed Reader-Writer Mutex by Dmitry Vyukov "aminer" <aminer@videotron.ca> - 2012-08-25 19:47 -0500
  Re: About Distributed Reader-Writer Mutex by Dmitry Vyukov "aminer" <aminer@videotron.ca> - 2012-08-25 20:01 -0500

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