Date: Sun, 21 Mar 2010 10:18:56 -0600 From: Scott Long <scottl@samsco.org> To: Andriy Gapon <avg@icyb.net.ua> Cc: Alexander Motin <mav@freebsd.org>, freebsd-current@freebsd.org, Ivan Voras <ivoras@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: Increasing MAXPHYS Message-ID: <082B2047-44AE-45DB-985B-D8928EBB4871@samsco.org> In-Reply-To: <4BA633A0.2090108@icyb.net.ua> References: <1269109391.00231800.1269099002@10.7.7.3> <1269120182.00231865.1269108002@10.7.7.3> <1269120188.00231888.1269109203@10.7.7.3> <1269123795.00231922.1269113402@10.7.7.3> <1269130981.00231933.1269118202@10.7.7.3> <1269130986.00231939.1269119402@10.7.7.3> <1269134581.00231948.1269121202@10.7.7.3> <1269134585.00231959.1269122405@10.7.7.3> <4BA6279E.3010201@FreeBSD.org> <4BA633A0.2090108@icyb.net.ua>
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m On Mar 21, 2010, at 8:56 AM, Andriy Gapon wrote: > on 21/03/2010 16:05 Alexander Motin said the following: >> Ivan Voras wrote: >>> Hmm, it looks like it could be easy to spawn more g_* threads (and, >>> barring specific class behaviour, it has a fair chance of working = out of >>> the box) but the incoming queue will need to also be broken up for >>> greater effect. >>=20 >> According to "notes", looks there is a good chance to obtain races, = as >> some places expect only one up and one down thread. >=20 > I haven't given any deep thought to this issue, but I remember us = discussing > them over beer :-) > I think one idea was making sure (somehow) that requests traveling = over the same > edge of a geom graph (in the same direction) do it using the same = queue/thread. > Another idea was to bring some netgraph-like optimization where some = (carefully > chosen) geom vertices pass requests by a direct call instead of = requeuing. >=20 Ah, I see that we were thinking about similar things. Another tactic, = and one that is easier to prototype and implement than moving GEOM to a graph, is to = allow separate but related bio's to be chained. If a caller, like maybe physio or the = bufdaemon or=20 even a middle geom transform, knows that it's going to send multiple = bio's at once, it chains them together into a single request, and that request gets = pipelined through the stack. Each layer operates on the entire chain before requeueing to = the next layer. Layers/classes that can't operate this way will get the bio serialized = automatically for them, breaking the chain, but those won't be the common cases. This will = bring cache locality benefits, and is something that know benefits high-transaction load = network applications. Scott
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