From: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> Date: Wed, 16 Oct 2024 10:56:44 +0200 > +netdev, I think we're starting to discuss more general things :) > > On Tue, 2024-10-15 at 17:49 -0700, Kuniyuki Iwashima wrote: > > From: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> > > Date: Tue, 15 Oct 2024 08:36:24 +0200 > > > On Mon, 2024-10-14 at 13:55 -0700, Kuniyuki Iwashima wrote: > > > > CONFIG_WEXT_CORE cannot be built as a module > > > > > > Isn't that precisely an argument for _not_ using net->gen[] with all the > > > additional dynamic allocations that implies? > > > > Exactly... > > > > Recently I was thinking most of the structs in struct net (except for > > first-class citizens like ipv4/ipv6) should use net->gen[] given the > > distro kernel enables most configs. > > Wait I'm confused, to me it seems you're contradicting yourself? :) Sorry, I meant the above is for module :) > > If we agree that making it use net->gen[] is more overhead since it > requires additional allocations (which necessarily require more memory > due to alignment etc., but even without that because now you needed > wext_net->net too) ... > > Then why do you think more should use net->gen[] if it's built-in? > > > But yes, WEXT is always built-in. > > I can see an argument for things that aren't always present, obviously, > like bonding and pktgen, but I don't see much of an argument for things > like wext that are either present or not? > > > Probably because wext_nlevents was just before a cacheline > > on my setup ? > > > > $ pahole -EC net vmlinux | grep net_generic -C 30 > > ... > > } wext_nlevents; /* 2536 24 */ > > /* --- cacheline 40 boundary (2560 bytes) --- */ > > struct net_generic * gen; /* 2560 8 */ > > I'd argue that doesn't really mean it makes sense to pull it into > net->gen (where it gets accessed via two indirect pointers)? > > That's an argument for reordering things there perhaps, but in struct > net that's probably not too much of an issue unless it shares a > cacheline with something that's used all the time? Yes, avoiding false shareing would be the only reason to use ->gen[] for builtin. I'll drop the patch 1 in v2. Btw, why WEXT cannot be module ?
