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Date: Tue, 8 Aug 2023 08:53:48 -0600
From: David Ahern <dsahern@...nel.org>
To: Ido Schimmel <idosch@...dia.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
edumazet@...gle.com, petrm@...dia.com
Subject: Re: [PATCH net 2/3] nexthop: Make nexthop bucket dump more efficient
On 8/8/23 1:52 AM, Ido Schimmel wrote:
> rtm_dump_nexthop_bucket_nh() is used to dump nexthop buckets belonging
> to a specific resilient nexthop group. The function returns a positive
> return code (the skb length) upon both success and failure.
>
> The above behavior is problematic. When a complete nexthop bucket dump
> is requested, the function that walks the different nexthops treats the
> non-zero return code as an error. This causes buckets belonging to
> different resilient nexthop groups to be dumped using different buffers
> even if they can all fit in the same buffer:
>
> # ip link add name dummy1 up type dummy
> # ip nexthop add id 1 dev dummy1
> # ip nexthop add id 10 group 1 type resilient buckets 1
> # ip nexthop add id 20 group 1 type resilient buckets 1
> # strace -e recvmsg -s 0 ip nexthop bucket
> [...]
> recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[...], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 64
> id 10 index 0 idle_time 10.27 nhid 1
> [...]
> recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[...], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 64
> id 20 index 0 idle_time 6.44 nhid 1
> [...]
>
> Fix by only returning a non-zero return code when an error occurred and
> restarting the dump from the bucket index we failed to fill in. This
> allows buckets belonging to different resilient nexthop groups to be
> dumped using the same buffer:
>
> # ip link add name dummy1 up type dummy
> # ip nexthop add id 1 dev dummy1
> # ip nexthop add id 10 group 1 type resilient buckets 1
> # ip nexthop add id 20 group 1 type resilient buckets 1
> # strace -e recvmsg -s 0 ip nexthop bucket
> [...]
> recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[...], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 128
> id 10 index 0 idle_time 30.21 nhid 1
> id 20 index 0 idle_time 26.7 nhid 1
> [...]
>
> While this change is more of a performance improvement change than an
> actual bug fix, it is a prerequisite for a subsequent patch that does
> fix a bug.
>
> Fixes: 8a1bbabb034d ("nexthop: Add netlink handlers for bucket dump")
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> Reviewed-by: Petr Machata <petrm@...dia.com>
> ---
> net/ipv4/nexthop.c | 16 +++++-----------
> 1 file changed, 5 insertions(+), 11 deletions(-)
>
Reviewed-by: David Ahern <dsahern@...nel.org>
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