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The devlink command to create an SF >>>> $ devlink port add pci/0000:03:00.0 flavour pcisf \ >>>> pfnum 0 sfnum 1001 >>>> takes around 5 seconds, and Linux perf and flamegraph show 19% of time >>>> spent on __dev_alloc_name() [1]. >>>> >>>> The reason is that devlink first requests for next available "eth%d". >>>> And __dev_alloc_name will scan all existing netdev to match on "ethN", >>>> set N to a 'inuse' bitmap, and find/return next available number, >>>> in our case eth0. >>>> >>>> And later on based on udev rule, we renamed it from eth0 to >>>> "en3f0pf0sf1001" and with altname below >>>> 14: en3f0pf0sf1001: ... >>>> altname enp3s0f0npf0sf1001 >>>> >>>> So eth0 is actually never being used, but as we have 1k "en3f0pf0sfN" >>>> devices + 1k altnames, the __dev_alloc_name spends lots of time goint >>>> through all existing netdev and try to build the 'inuse' bitmap of >>>> pattern 'eth%d'. And the bitmap barely has any bit set, and it rescanes >>>> every time. >>>> >>>> I want to see if it makes sense to save/cache the result, or is there >>>> any way to not go through the 'eth%d' pattern search. The RFC patch >>>> adds name_pat (name pattern) hlist and saves the 'inuse' bitmap. It saves >>>> pattens, ex: "eth%d", "veth%d", with the bitmap, and lookup before >>>> scanning all existing netdevs. >>> An alternative heuristic that should be cheap and possibly reasonable >>> could be optimistically check for 0.. >>> availability, possibly restricting such attempt at scenarios where the >>> total number of hashed netdevice names is somewhat high. >>> >>> WDYT? >>> >>> Cheers, >>> >>> Paolo >> Hi Paolo, >> >> Thanks for your suggestion! >> I'm not clear with that idea. >> >> The current code has to do a full scan of all netdevs in a list, and the >> name list is not sorted / ordered. So to get to know, ex: eth0 .. eth10, >> we still need to do a full scan, find netdev with prefix "eth", and get >> net available bit 11 (10+1). >> And in another use case where users doesn't install UDEV rule to rename, >> the system can actually create eth998, eth999, eth1000.... >> >> What if we create prefix map (maybe using xarray) >> idx entry=(prefix, bitmap) >> -------------------- >> 0 eth, 1111000000... >> 1 veth, 1000000... >> 2 can, 11100000... >> 3 firewire, 00000... >> >> but then we need to unset the bit when device is removed. >> William > Sorry for the late reply. I mean something alike the following > (completely untested!!!): > --- > diff --git a/net/core/dev.c b/net/core/dev.c > index d2ce91a334c1..0d428825f88a 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -1109,6 +1109,12 @@ static int __dev_alloc_name(struct net *net, const char *name, char *res) > if (!p || p[1] != 'd' || strchr(p + 2, '%')) > return -EINVAL; > > + for (i = 0; i < 4; ++i) { > + snprintf(buf, IFNAMSIZ, name, i); > + if (!__dev_get_by_name(net, buf)) > + goto found; > + } > + > /* Use one page as a bit array of possible slots */ > inuse = bitmap_zalloc(max_netdevices, GFP_ATOMIC); > if (!inuse) > @@ -1144,6 +1150,7 @@ static int __dev_alloc_name(struct net *net, const char *name, char *res) > if (i == max_netdevices) > return -ENFILE; > > +found: > /* 'res' and 'name' could overlap, use 'buf' as an intermediate buffer */ > strscpy(buf, name, IFNAMSIZ); > snprintf(res, IFNAMSIZ, buf, i); > > --- > plus eventually some additional check to use such heuristic only if the > total number of devices is significantly high. That would need some > additional book-keeping, not added here. > > Cheers, > > Paolo Hi Paolo, Thanks, now I understand the idea. Will give it a try. William >