[openib-general] Re: uverbs events

[ardavis]

Roland Dreier wrote:

>    ardavis> Redhat EL 4.0, 64-bit
>
>OK, I found a system with that distro installed, although I can't test
>the results of the build.  However, I built libmthca with the same
>CFLAGS that rpm seems to use, namely "-g -O2 -m64 -pipe".  I found
>that mthca_tavor_arm_cq() compiles to the following tiny fragment:
>
>0000000000001d10 <mthca_tavor_arm_cq>:
>    1d10:       48 8b 07                mov    (%rdi),%rax
>    1d13:       48 8b 90 a8 ef ff ff    mov    0xffffffffffffefa8(%rax),%rdx
>    1d1a:       48 8b 44 24 f8          mov    0xfffffffffffffff8(%rsp),%rax
>    1d1f:       48 89 42 20             mov    %rax,0x20(%rdx)
>    1d23:       31 c0                   xor    %eax,%eax
>    1d25:       c3                      retq
>
>in other words, the compiler seems to be discarding all the
>assignments to doorbell[0] and doorbell[1].  I'm not sure if this is a
>compiler bug or what -- I need to investigate further.  In any case
>can you try the following patch to libmthca and see if it fixes
>things:
>
>Index: src/cq.c
>===================================================================
>--- src/cq.c	(revision 2156)
>+++ src/cq.c	(working copy)
>@@ -441,6 +441,8 @@ int mthca_tavor_arm_cq(struct ibv_cq *cq
> 			    to_mcq(cq)->cqn);
> 	doorbell[1] = 0xffffffff;
> 
>+	mb();
>+
> 	mthca_write64(doorbell, to_mctx(cq->context), MTHCA_CQ_DOORBELL);
> 
> 	return 0;
>
>  
>
Yes, this fixes my problem. Thanks!