From: Eric Dumazet <eric.dumazet@gmail.com>
To: Hangbin Liu <liuhangbin@gmail.com>, netdev@vger.kernel.org
Cc: Stephen Hemminger <stephen@networkplumber.org>,
Michal Kubecek <mkubecek@suse.cz>, Phil Sutter <phil@nwl.cc>
Subject: Re: [PATCHv5 iproute2 net-next 2/2] lib/libnetlink: re malloc buff if size is not enough
Date: Tue, 12 Feb 2019 15:43:24 -0800 [thread overview]
Message-ID: <4e327b7c-fc1f-ea3a-ba2a-54d81493ba62@gmail.com> (raw)
In-Reply-To: <244174ae-3ab4-68c0-6783-f8c91840a7e1@gmail.com>
On 02/12/2019 03:32 PM, Eric Dumazet wrote:
>
>
> This patch brings a serious performance penalty.
>
> ss command now uses two system calls per ~4KB worth of data
>
> recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{NULL, 0}], msg_controllen=0, msg_flags=MSG_TRUNC}, MSG_PEEK|MSG_TRUNC) = 3328 <0.000120>
> recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"h\0\0\0\24\0\2\0@\342\1\0\322\0\6\0\n\1\1\0\250\253\276@&\7\370\260\200\231\16\6"..., 3328}], msg_controllen=0, msg_flags=0}, 0) = 3328 <0.000108>
> recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{NULL, 0}], msg_controllen=0, msg_flags=MSG_TRUNC}, MSG_PEEK|MSG_TRUNC) = 3328 <0.000086>
> recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"h\0\0\0\24\0\2\0@\342\1\0\322\0\6\0\n\10\2\0002A\266S&\7\370\260\200\231\16\6"..., 3328}], msg_controllen=0, msg_flags=0}, 0) = 3328 <0.000121>
>
>
> So we are back to a very pessimistic situation.
>
I guess this patch will solve the issue :
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index ced33728777a17e0905e76acb904ac4709707488..309b5b3787e3d8f8c47f035d270ae2b4df01703e 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -442,6 +442,8 @@ static int rtnl_recvmsg(int fd, struct msghdr *msg, char **answer)
if (len < 0)
return len;
+ if (len < 32768)
+ len = 32768;
buf = malloc(len);
if (!buf) {
fprintf(stderr, "malloc error: not enough buffer\n");
next prev parent reply other threads:[~2019-02-12 23:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 1:41 [PATCHv5 iproute2 net-next 0/2] libnetlink: malloc correct buff at run time Hangbin Liu
2017-10-26 1:41 ` [PATCHv5 iproute2 net-next 2/2] lib/libnetlink: re malloc buff if size is not enough Hangbin Liu
2017-10-26 2:59 ` David Ahern
2017-10-26 10:24 ` Stephen Hemminger
2017-10-26 15:28 ` David Ahern
2017-10-26 15:33 ` Phil Sutter
2017-10-26 15:42 ` David Ahern
2017-10-26 18:31 ` Phil Sutter
2019-02-12 23:32 ` Eric Dumazet
2019-02-12 23:43 ` Eric Dumazet [this message]
2017-10-26 1:41 ` [PATCHv5 iproute2 net-next 2/2] lib/libnetlink: update rtnl_talk to support malloc buff at run time Hangbin Liu
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