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iser: support rdma ack timeout optimization

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Since 2c1619edef61a03cb516efaa81750784c3071d10 for linux kernel and
55843c4ab8f559679d28c559cc4d681836be769b for rdma-core, rdma cma
supports RDMA_OPTION_ID_ACK_TIMEOUT. It's useful for RDMA out of
sequence case. Because this feature is added recently, we have to
check this in autogen.sh before building source code.

Depend on production enviroument, tunning rdma ack timeout could get
the best performance. Suggested by Bart and Ronnie, instead of using
a fixed timeout value, add two methods to set rdma ack timeout value.
1, add URL variable 'LIBISCSI_RDMA_ACK_TIMEOUT'. This could works
for a specified connection.
2, add env argument 'LIBISCSI_RDMA_ACK_TIMEOUT'. This works as a
common setting for all the connection of a process.

Test under different packet loss rate and different ack timeout, run
fio (iodepth=1) in a guest os, I got this result:
latency under packet loss rate 0.00001:
	timeout 19: avg 170.22, pct99.9 215
	timeout 10: avg 160.08, pct99.9 215
	timeout 8 : avg 146.39, pct99.9 177
	timeout 7 : avg 148.37, pct99.9 211

latency under packet loss rate 0.0001:
	timeout 19: avg 949.23, pct99.9 306
	timeout 10: avg 818.53, pct99.9 378
	timeout 8 : avg 615.84, pct99.9 189
	timeout 7 : avg 618.89, pct99.9 310

Base on this test report, setting ack timeout to 8(1048.576 usec) is
a good choice in my test enviroument.

Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
This commit is contained in:
zhenwei pi
2020-03-02 10:50:12 +08:00
committed by Bart Van Assche
parent e051995303
commit 6ed1ffb7b2
4 changed files with 53 additions and 0 deletions
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2
include/iscsi-private.h
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@@ -109,6 +109,8 @@ struct iscsi_context {
int tcp_syncnt;
int tcp_nonblocking;
unsigned char rdma_ack_timeout;
int current_phase;
int next_phase;
#define ISCSI_LOGIN_SECNEG_PHASE_OFFER_CHAP 0