David Miller wrote:
From: Linus Torvalds <[EMAIL PROTECTED]>
Date: Thu, 7 Feb 2008 09:42:56 -0800 (PST)
Can we please just stop doing these one-by-one assignments, and just do
something like
memset(rq, 0, sizeof(*rq));
rq->q = q;
rq->ref_count = 1;
INIT_HLIST_NODE(&rq->hash);
RB_CLEAR_NODE(&rq->rb_node);
instead?
The memset() is likely faster and smaller than one-by-one assignments
anyway, even if the one-by-ones can avoid initializing some field or there
ends up being a double initialization..
The problem is store buffer compression. At least a few years
ago this made a huge difference in sk_buff initialization in the
networking.
Maybe cpus these days have so much store bandwith that doing
things like the above is OK, but I doubt it :-)
on modern x86 cpus the memset may even be faster if the memory isn't in cache;
the "explicit" method ends up doing Write Allocate on the cache lines
(so read them from memory) even though they then end up being written entirely.
With memset the CPU is told that the entire range is set to a new value, and
the WA can be avoided for the whole-cachelines in the range.
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