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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2024-05-06 at 20:32 +0000, William Tu wrote: > When a system has around 1000 netdevs, adding the 1001st device becomes > very slow. 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]. >=20 > 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. >=20 > And later on based on udev rule, we renamed it from eth0 to > "en3f0pf0sf1001" and with altname below > 14: en3f0pf0sf1001: ... > altname enp3s0f0npf0sf1001 >=20 > 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. >=20 > 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=C2=A00.. availability, possibly restricting such attempt at scenarios where the total number of hashed netdevice names is somewhat high. WDYT? Cheers, Paolo