On Mon, Feb 13, 2017 at 01:24:36PM -0800, Paul E. McKenney wrote: > On Mon, Feb 13, 2017 at 04:06:21PM -0500, Alan Stern wrote: > > On Mon, 13 Feb 2017, Paul E. McKenney wrote: > > > > > On Mon, Feb 13, 2017 at 08:14:23PM +0100, Tobias Klausmann wrote: > > > > Hi! > > > > > > > > On Mon, 13 Feb 2017, Paul E. McKenney wrote: > > > > > On Mon, Feb 13, 2017 at 01:53:27PM -0500, bob smith wrote: > > > > > > On 2/13/17 1:39 PM, Paul E. McKenney wrote: > > > > > > > can real DEC Alpha hardware end up with both instances of "r1" > > > > > > > having the value 1? > > > > > > > > > > > > I thought this question reminded me of something, so I found this: > > > > > > > https://www.kernel.org/doc/Documentation/memory-barriers.txt > > > > > > > > > > > > and I pasted in the content - David Howells is one of the authors and > > > > > > maybe that is why the question sort of reminded me. > > > > > > > > > > > > Maybe someone has an update but this is what was said then. > > > > > > > > > > Well, thank you for pointing me to this, but my question was intended to > > > > > check whether or not the words I helped to write in memory-barriers.txt > > > > > are in fact accurate. So if you have an SMP DEC Alpha system that you > > > > > could provide remote access to, that would be very helpful! > > > > > > > > I have a 4-cpu ES40. Send me a test program and I'll gladly run > > > > it for you. > > > > > > Andrea, could you please convert the litmus test below and send it to > > > Tobias? > > > > > > Thanx, Paul > > > > > > ------------------------------------------------------------------------ > > > > > > C auto/C-LB-LRW+OB-Dv > > > (* > > > * Result: Never > > > * > > > *) > > > { > > > } > > > > > > P0(int *u0, int *x1) > > > { > > > r1 = READ_ONCE(*u0); > > > smp_mb(); > > > WRITE_ONCE(*x1, 1); > > > } > > > > > > > > > P1(int *u0, int *x1) > > > { > > > r1 = rcu_dereference(*x1); > > > > No, please, not this. It should be: > > > > r1 = READ_ONCE(*x1); > > > > That is, the auto/C-LB-LRW+OB-Ov.litmus test. > > > > > WRITE_ONCE(*u0, r1); > > > } > > > > > > exists > > > (0:r1=1 /\ 1:r1=1) > > Sorry, here is the correct one in full. > > Thanx, Paul > > ------------------------------------------------------------------------ > > C auto/C-LB-LRW+OB-Ov > (* > * Result: Maybe > * P0-P1 rf OB-Ov: Never->Maybe: Note lack of C11 guarantee, control dependency > * P1 Ov,LRW: Note lack of C11 guarantee, control dependency > *) > { > } > > P0(int *u0, int *x1) > { > r1 = READ_ONCE(*u0); > smp_mb(); > WRITE_ONCE(*x1, 1); > } > > > P1(int *u0, int *x1) > { > r1 = READ_ONCE(*x1); > WRITE_ONCE(*u0, r1); > } > > exists > (0:r1=1 /\ 1:r1=1) > The (automatically generated) module for this test is at http://retis.sssup.it/~a.parri/lkmm/C-LB-LRW+OB-Ov.tgz ; the test is run by cat-ing /sys/kernel/litmus/p_count: this will execute the thread bodies for "runs * size" iterations; results can be sentisive to the "stride" and "affinity increment" parameters (c.f., the Makefile); statistics for each experiments are printed on stdout. Please let me know should you find any problem with this. Thank you, Andrea Disclaimer: I'm not "excited", to use an euphemism, to post such an ugly C code to LKML ...; _most importantly_, I've certainly never tested this on any Alpha machine ... -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
