[libvirt][PATCH v2] libvirtd: Increase NL buffer size for lots of
interface has been sent.
Appreciated your comment and review. Thanks
On 2016年01月07日 02:25, Laine Stump wrote:
Now that everyone is back from holidays, I wanted to revisit this
patch (since the message I'm replying to contains most of the
discussion, but not the original patch, I've attached it at the end)
and hopefully get input from Tomas Graf about whether or not the
problems with netlink/libnl noted in the commit message that prevent
proper operation of message peeking are eliminated in recent versions
(if so, then I think the "128k buffer + enable peeking" you propose
will be a proper permanent fix.)
Also, in the message referenced below I had asked a question about the
"LTC-Bugzilla" references, and pointed out that your patch only works
with libnl3 (not libnl-1.1) and only fixes the problem in one of
several places that libvirt uses libnl to create a netlink socket in
this message, then suggested a method of making a general purpose fix
for all uses an all versions of libnl:
https://www.redhat.com/archives/libvir-list/2015-December/msg00697.html
Can you create a new version of the patch that provides a general
solution as suggested (or similar) and either gives a clickable link
to the referenced LTC-Bugzilla issues or removes the reference (former
is preferred)?
Thanks!
On 12/20/2015 05:06 PM, Laine Stump wrote:
On 12/18/2015 02:30 AM, Leno Hou wrote:
On 2015年12月17日 02:33, Laine Stump wrote:
On 12/16/2015 10:24 AM, Michal Privoznik wrote:
On 10.12.2015 07:34, Leno Hou wrote:
1. When switching CPUs to offline/online in a system more than
128 cpus
2. When using virsh to destroy domain in a system with more
interface
All of above happens nl_recv returned with error: No buffer space
available.
This patch set socket buffer size to 128K and turn on message
peeking for nl_recv,
as this would solve this problem totally and permanetly.
Signed-off-by: Leno Hou <ho...@linux.vnet.ibm.com>
Cc: Wenyi Gao <we...@linux.vnet.ibm.com>
---
src/util/virnetlink.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/src/util/virnetlink.c b/src/util/virnetlink.c
index 679b48e..c8c9fe0 100644
--- a/src/util/virnetlink.c
+++ b/src/util/virnetlink.c
@@ -696,6 +696,14 @@ virNetlinkEventServiceStart(unsigned int
protocol, unsigned int groups)
goto error_server;
}
+ if (nl_socket_set_buffer_size(srv->netlinknh, 131702, 0) <
0) {
The above function doesn't exist in libnl 1.1 (still used in
RHEL6/CentOS6, for example), so that would cause a build failure on
some systems. In libnl 1.1 the function is called
nl_set_buffer_size().
Also, how did you arrive at 128k for the default buffer size? What
kind of sizes are you seeing?
This buffer size is the receive socket buffer size. When I switching
CPUs to offline/online, it's receives 107K.
Wow! What is in this message, and where/how is it used in the code?
+ virReportSystemError(errno,
+ "%s",_("cannot set netlink socket buffer size to
128k"));
+ goto error_server;
+ }
+
+ nl_socket_enable_msg_peek(srv->netlinknh);
+
According to a link I followed from another message on this topic
last week, libnl's message peeking can't be guaranteed to always
work, because netlink doesn't always return the proper buffer size
(depending on version).
I would not use message peeking due to I agree with you on that
message peeking can't be guaranteed to always work.
I'm hoping that is only for "older" versions of kernel/netlink/libnl.
Thomas?
if ((srv->eventwatch = virEventAddHandle(fd,
VIR_EVENT_HANDLE_READABLE,
virNetlinkEventCallback,
I believe this patch appears over and over again. Usually, the
problem
was in libnl library we use and this was just a workaround. Can
you test
with the latest libnl version (probably even GIT HEAD) and see if
that
helps?
I had the same memory. So I just looked back through the history of
bug reports about this issue, and found the following:
* libnl-1.1 and libnl-3 both originally set the default message
buffersize to 4096 bytes, with MSG_PEEK turned off.
* when this problem came up in RHEL6, it was unfortunately reported
as a private BZ (a pet peeve of mine), and the result of the
discussion about it was that libnl-1.1 (the version used in RHEL6)
was patched *upstream* to set the default message buffersize to
16384 bytes (getpagesize() * 4), which would solve the problem for
even very large numbers of VFs. That was in 2013 and there have
been no further reports against RHEL6.
* Although I had assumed the problem was solved, it again came up
in RHEL7 (which uses libnl-3 - a slightly different API, and
maintained in a separate git repo), this time in a public BZ:
https://bugzilla.redhat.com/show_bug.cgi?id=1040626
I'm not familar with this bug :-( I think this maybe different
from my case.
Well, I wasn't even aware that libvirt's netlink service was used for
CPU hotplug (and still don't see how/where that happens) :-)
The above bug reports were due to 4096 bytes not being enough to read
an entire IFLA_VF_PORTS array.
I asked if perhaps the change that had been made upstream in
libnl-1.1 hadn't also been made to libnl-3 (this is what I assumed
during the previous incident). It hadn't. So the same change was
made for libnl-3, both upstream and as a backport to RHEL7, and
everyone was happy.
I have very little detailed memory of that time (the above was all
recalled by looking at archives of discussions) but what had stuck
in my mind was "This problem has been fixed in libnl, so libvirt
should NOT put in "workarounds" for broken versions of libnl."
But if you are using a version of libnl3 with this patch (which was
in libnl-3.2.22 upstream, and is in the libnl-3.2.21 that's in
RHEL7.0+), :
https://github.com/tgraf/libnl/commit/807fddc4cd9ecb12ba64e1b7fa26d86b6c2f19b0
This patch sets *message* buffer size to 4 pages. But I'm prefer to
say I wanna to set *socket* buffer size to 128k
then the change to quadruple the buffer size in libnl was
insufficient, (and also, when I looked back at the discussion now,
> I see that the libnl maintainer had said "The permanent fix would
be for libvirt to enable message peeking", so I suppose it's time
to "bite the bullet" and enable netlink message
Yes, I would to set socket buffer size in libvirt because If we can
set socket buffer size in libnl, it's can give impact on the app
that do not need 128K socket buffer size.
Yes. 16K is one thing, but 128K is quite a lot more, and could more
easily cause a problem with other applications.
peeking in libvirt (but, since there are apparently versions of
netlink that don't properly inform libnl when a re-read is
necessary, we also need to increase the default buffer size).
However, your patch is only fixing the problem in one place. There
are several places that we allocate netlink sockets, and they
should all get the same fix, implying that there should be a common
function called by all three. Fortunately, we already have a macro
called "virNetlinkAlloc" that is #defined differently depending on
the libnl version - this macro can simply be made into a static
function that is defined differently depending on libnl version. It
can call nl_handle_alloc or nl_socket_alloc depending on libnl
version, then call nl_socket_set_buffer_size/nl_set_buffer_size
depending on version, and finally call nl_socket_enable_msg_peek.
A bit of due diligence about the default buffer size is in order
though - just to make sure that we don't open a ton of netlink
sockets at the same time, each with an unnecessarily huge buffer.
Does anyone has an good idea to solve this problem permanently?
i.e. Dynamically allocate the socket buffer size accordingly. Thanks
I *think* (based on the things I've read, not on personal experience)
that sufficiently new versions of libnl and kernel *do* properly
implement message peeking, so we can just start off with a buffer
size larger than what we think will ever be needed on a current
system, and also enable message peeking, which should future-proof
the code (so, basically what you've done). I'm Cc'ing Thomas Graf
(from libnl) for his opinion though.
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