From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Wagner Subject: Re: [PATCH 4/7] netprio_cgroup: reimplement priomap expansion Date: Tue, 20 Nov 2012 16:09:22 +0100 Message-ID: <50AB9D22.5030000@monom.org> References: <1353400211-5182-1-git-send-email-tj@kernel.org> <1353400211-5182-5-git-send-email-tj@kernel.org> <50AB435E.8060901@monom.org> <20121120143832.GO15971@htj.dyndns.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20121120143832.GO15971-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Tejun Heo Cc: serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org, ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org, nhorman-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org, tgraf-G/eBtMaohhA@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 20.11.2012 15:38, Tejun Heo wrote: > Hello, Daniel. > > On Tue, Nov 20, 2012 at 09:46:22AM +0100, Daniel Wagner wrote: >> struct netprio_map { >> struct rcu_head rcu; >> struct netprio_aux *aux; /* auxiliary config array */ >> u32 priomap_len; >> u32 priomap[]; >> }; >> >> Is there a specific reason why aux and priomap is handled >> differently? Couldn't you just use same approach for both variables, >> e.g. re/allocating only them here and leave the allocation struct >> netprio_map in cgrp_css_alloc()? > > ->aux is no longer added, so the consistency issue doesn't exist > anymore. Right, I got confused looking at v1 and v2. > The reason why they were handled differently before (or > rather why I didn't change priomap[] to be allocated separately) was > that pointer chasing tends to be more expensive than offsetting. I > don't know how much effect it would have in this case but things > sitting in packet in/out paths can be very hot so didn't wanna disturb > it. I see. >> Also the algorithm to figure out the size of the array might be a >> bit too aggressive in my opinion. So you always start at >> PRIOMAP_MIN_SIZE and then try to double the size until target_idx >> fits. Wouldn't it make sense to start to look for the new size >> beginning at old->priomap_len and then do the power-of-two increase? > > The only downside of always starting from PRIOMAP_MIN_SIZE is > iterating several more times in the sizing loop which isn't really > anything to worry about. The loop is structured that way because I > wanted to keep the size of the whole thing power-of-two. Due to the > fields before priomap[], if we size priomap_len power-of-two, we'll > always end up with something slightly over power-of-two, which is > usually the worst size to allocate. Thanks for the explanation. I was pondering if the new size in power of two could be a bit too excessive and the allocation step could be linear, e.g. stick at 4096. target_id will increase linear, therefore linear increase might also be enough, no? cheers, daniel