[dpdk-dev] [PATCH] keepalive: fix keepalive state alignment

Van Haaren, Harry harry.van.haaren at intel.com
Tue Jan 23 11:27:40 CET 2018


> From: Horton, Remy
> Sent: Tuesday, January 23, 2018 10:17 AM
> To: Andriy Berestovskyy <aber at semihalf.com>; Van Haaren, Harry
> <harry.van.haaren at intel.com>
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] keepalive: fix keepalive state alignment
> 
> 
> On 22/01/2018 18:20, Andriy Berestovskyy wrote:
> [..]
> > On Fri, Jan 19, 2018 at 6:31 PM, Van Haaren, Harry
> > <harry.van.haaren at intel.com> wrote:
> >> These changes do reduce false-sharing however is there actually a
> >> performance benefit? A lot of cache space will be taken up if each
> >> core requires its own cache line, which will reduce performance
> >> again.. it's a tradeoff.
> [..]
> > 2. The original code (prior e70a61ad50ab "keepalive: export states")
> > had each element aligned to the cache line, not the whole array.
> 
> Aligning each flag element was the original intention, so I see no issue
> in restoring it. The monitoring core only reads the entries within
> state_flags for which the corresponding active_core is set, so
> ultimately the trade-off in cache line usage is one made by the
> application when it decides which cores need monitoring.
> 
> ..Remy

No objection here - just making sure the change was intentional
and the effects are considered.

@Remy as you're the Keepalive maintainer I'll leave Acking to you :)

-Harry


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