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Re: [PATCH][SPARC] missing membar in niagara2_memcpy
- From: jose dot marchesi at oracle dot com (Jose E. Marchesi)
- To: David Miller <davem at davemloft dot net>
- Cc: libc-alpha at sourceware dot org
- Date: Thu, 15 May 2014 19:31:43 +0200
- Subject: Re: [PATCH][SPARC] missing membar in niagara2_memcpy
- Authentication-results: sourceware.org; auth=none
- References: <87k39n6mtn dot fsf at oracle dot com> <20140515 dot 125521 dot 925272462801829164 dot davem at davemloft dot net>
> Tested on an Athena machine (sparc64x) running sparc64-*-linux-gnu.
> No new warnings triggered by the patch.
> No regressions detected.
Does it really fix anything?
Are these crashes or data corruptions or thread data visibilty issues
that you've seen in practice and are cured by this change?
Several system tests of a certain (very data intensive) program crashed
as soon as it started to use multilib/niagara2_memcpy, due to memory
corruption. They run just fine after this patch is applied.
We also observed that jar would occasionally raise
java.util.zip.ZipException. This was due to the fact the last two bytes
of a buffer were not apparently being copied by memcpy. Again, this
patch fixes that problem.
The member is extremely expensive and I avoided it intentionally.
Yes I suspected that, given how carefully that code is written. We are
aware that membars are painful on the T2 (any membar, because all
flavors are mapped to #Sync) but the risk of overlaps is not only
theoretical in this case, unfortunately :(