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tcp: double default TSQ output bytes limit
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Xen virtual network driver has higher latency than a physical NIC.
Having only 128K as limit for TSQ introduced 30% regression in guest
throughput.

This patch raises the limit to 256K. This reduces the regression to 8%.
This buys us more time to work out a proper solution in the long run.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Wei Liu authored and David S. Miller committed Jun 4, 2015
1 parent 12e25e1 commit c39c4c6
Showing 1 changed file with 2 additions and 2 deletions.
4 changes: 2 additions & 2 deletions net/ipv4/tcp_output.c
Original file line number Diff line number Diff line change
Expand Up @@ -50,8 +50,8 @@ int sysctl_tcp_retrans_collapse __read_mostly = 1;
*/
int sysctl_tcp_workaround_signed_windows __read_mostly = 0;

/* Default TSQ limit of two TSO segments */
int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
/* Default TSQ limit of four TSO segments */
int sysctl_tcp_limit_output_bytes __read_mostly = 262144;

/* This limits the percentage of the congestion window which we
* will allow a single TSO frame to consume. Building TSO frames
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