On 11/08/2018 12:23 AM, Jean-Louis Dupond wrote:
> Hi,
>
> Was somebody able to check this?
> Really think this should be fixed :)
>
> Thanks
> Jean-Louis
>
I somehow missed this email.
Packet captures might help, please send me
tcpdump -s 128 -i ethX -w sack.pcap
of some samples with or without the sack compression enabled.
> On 3/11/18 16:59, Jean-Louis Dupond wrote:
>> Hi All,
>>
>> On recent kernels we noticed a way lower throughput to our SAN system than
>> before.
>> While on pre 4.18 kernels we had 400-700MB/sec read speed, on 4.18+ we only
>> had 70-120MB/sec.
>>
>> The SAN is connected via iSCSI over a 10G network (ixgbe/X520 NICS if it
>> matters).
>>
>> After some debugging, I tried to bisect between 4.17 and 4.18 to see what
>> commit caused the slowdown.
>> It showed that the addition of the SACK compression
>> (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5d9f4262b7ea41ca9981cc790e37cca6e37c789e)
>> was the cause.
>>
>> And indeed, if I set net.ipv4.tcp_comp_sack_nr to 0 on 4.19 for example, the
>> throughput is (almost) back to normal again.
>> So it seems like this change causes quite some performance issues.
>>
>> Any ideas?
>>
>> Thanks
>> Jean-Louis
>>
