On Sun, 2012-11-25 at 22:44 -0800, Eric Dumazet wrote: > On Mon, 2012-11-26 at 11:29 +0800, ling.ma.prog...@gmail.com wrote: > > From: Ma Ling <ling.ma.prog...@gmail.com> > > > > In order to reduce memory latency when last level cache miss occurs, > > modern CPUs i.e. x86 and arm introduced Critical Word First(CWF) or > > Early Restart(ER) to get data ASAP. For CWF if critical word is first member > > in cache line, memory feed CPU with critical word, then fill others > > data in cache line one by one, otherwise after critical word it must > > cost more cycle to fill the remaining cache line. For Early First CPU will > > restart until critical word in cache line reaches. > > > > Hash value is critical word, so in this patch we place it as first member > > in cache line(sock address is cache-line aligned), and it is also good for > > Early Restart platform as well . > > > > Thanks > > Ling > > networking patches should be sent to netdev. > > (I understand this patch is more a generic one, but at least CC netdev) > > You give no performance numbers for this change... > > I never heard of this CWF/ER, where are the official Intel documents > about this, and what models really benefit from it ? [...]
CWF is a standard feature of SDRAM. Ulrich Drepper's series of articles on memory covers this in part 2 <http://lwn.net/Articles/252125/> section 3.5.2. As for whether it's slower to start fetching from the middle, that may depend on the memory controller and memory type that are used. Drepper's benchmark showed only a small penalty (<1%) for fetching from the middle, though he didn't say anything particular about the hardware configuration. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
