[libvirt] [PATCH v3] libvirtd: Increase NL buffer size for lots of interface

[Laine Stump]

On 01/11/2016 05:44 AM, Martin Kletzander wrote:
> On Mon, Jan 11, 2016 at 02:59:00PM +0800, 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 sets the socket buffer size to 128K and turns on message 
>> peeking
>> for nl_recv,as this would solve this problem totally and permanetly.
>>
>
> So if none of the above is true/happening...
>
>> Signed-off-by: Leno Hou <houqy at linux.vnet.ibm.com>
>> Cc: Wenyi Gao <wenyi at linux.vnet.ibm.com>
>> CC: Laine Stump <laine at laine.org>
>> CC: Michal Privoznik <mprivozn at redhat.com>
>> ---
>> src/util/virnetlink.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/src/util/virnetlink.c b/src/util/virnetlink.c
>> index 679b48e..ea65cbc 100644
>> --- a/src/util/virnetlink.c
>> +++ b/src/util/virnetlink.c
>> @@ -65,10 +65,12 @@ struct virNetlinkEventHandle {
>>
>> # ifdef HAVE_LIBNL1
>> #  define virNetlinkAlloc nl_handle_alloc
>> +#  define virSocketSetBufferSize nl_set_buffer_size
>> #  define virNetlinkFree nl_handle_destroy
>> typedef struct nl_handle virNetlinkHandle;
>> # else
>> #  define virNetlinkAlloc nl_socket_alloc
>> +#  define virSocketSetBufferSize nl_socket_set_buffer_size
>> #  define virNetlinkFree nl_socket_free
>> typedef struct nl_sock virNetlinkHandle;
>> # endif
>> @@ -696,6 +698,14 @@ virNetlinkEventServiceStart(unsigned int 
>> protocol, unsigned int groups)
>>         goto error_server;
>>     }
>>
>> +    if (virSocketSetBufferSize(srv->netlinknh, 131702, 0) < 0) {
>> +        virReportSystemError(errno,
>> +                "%s",_("cannot set netlink socket buffer size to 
>> 128k"));
>> +        goto error_server;
>> +    }
>> +
>> +    nl_socket_enable_msg_peek(srv->netlinknh);
>> +
>
> ... shouldn't this be non-fatal just in case?

I at first agreed with this [*] if we just issue a warning and continue 
we would have the least possibility of regression on older systems (or 
maybe some odd/old system that didn't allow setting a 128k buffer?). But 
on the other hand, I think the likelyhood of this is very low, and if it 
*does* happen we (the developers/maintainers) want to know about it. If 
there's a warning in a log file and libvirt continues to operate, the 
user isn't likely to report it. If there is an error message and 
something doesn't work, then we will definitely hear about it. So I 
think this should remain as an error.

Any other opinions?

BTW, otherwise ACK on the change - I backported it to libvirt-0.10.2 and 
it built on RHEL6 (which uses libnl1) without problem.



[*](every other error condition in virNetlinkEvenServiceStart() is due 
to a condition that would make the netlink listener completely 
non-functional, so it makes sense to shut it down. But if we failed to 
set the socket buffer size as requested, it would still function on 
*most* systems.


>
>>     if ((srv->eventwatch = virEventAddHandle(fd,
>> VIR_EVENT_HANDLE_READABLE,
>> virNetlinkEventCallback,
>> -- 
>> 1.9.1
>>
>> -- 
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