Re: REGRESSION f54b311142a92ea2e42598e347b84e1655caf8e3 tcp autocorking slows down iSCSI file system creation by factor of 70 [WAS: 4 TBVMFS creation takes 15 minutes vs 26 seconds]

[Eric Dumazet]

On Sat, 2014-02-08 at 05:50 -0800, Eric Dumazet wrote:
> On Sat, 2014-02-08 at 05:33 -0800, Eric Dumazet wrote:
> > On Sat, 2014-02-08 at 05:14 -0800, Eric Dumazet wrote:
> > > Here is the combined patch, could you test it ?
> > 
> > Also make sure you have commit a181ceb501b31b4bf8812a5c84c716cc31d82c2d
> > ("tcp: autocork should not hold first packet in write queue")
> > in your tree.
> > 
> > 
> 
> BTW this problem demonstrates there is room for improvement in iCSCI,
> using MSG_MORE to avoid sending two small segments in separate frames.
> 
> [1] 00:32:35.726568 IP 10.101.99.5.3260 > 10.101.0.13.27778: Flags [P.], seq 145:193, ack 144, win 235, options [nop,nop,TS val 4294960733 ecr 385385], length 48
> [2] 00:32:35.838074 IP 10.101.0.13.27778 > 10.101.99.5.3260: Flags [.], ack 193, win 514, options [nop,nop,TS val 385396 ecr 4294960733], length 0
> [3] 00:32:35.838099 IP 10.101.99.5.3260 > 10.101.0.13.27778: Flags [P.], seq 193:705, ack 144, win 235, options [nop,nop,TS val 4294960761 ecr 385396], length 512
> 
> [1] & [3] could be coalesced, and [2] would be avoided.
> 

With the fix, new pcap is more explicit about this suboptimal behavior :

05:34:16.280900 IP 10.101.0.13.41531 > 10.101.99.5.3260: Flags [.], ack 54353, win 514, options [nop,nop,TS val 1732452 ecr 4294935370], length 0
05:34:16.280949 IP 10.101.0.13.41531 > 10.101.99.5.3260: Flags [P.], seq 5328:5376, ack 54353, win 514, options [nop,nop,TS val 1732452 ecr 4294935370], length 48

05:34:16.280982 IP 10.101.99.5.3260 > 10.101.0.13.41531: Flags [P.], seq 54353:54401, ack 5376, win 235, options [nop,nop,TS val 4294935370 ecr 1732452], length 48
05:34:16.281000 IP 10.101.99.5.3260 > 10.101.0.13.41531: Flags [P.], seq 54401:54913, ack 5376, win 235, options [nop,nop,TS val 4294935370 ecr 1732452], length 512

05:34:16.281107 IP 10.101.0.13.41531 > 10.101.99.5.3260: Flags [.], ack 54913, win 514, options [nop,nop,TS val 1732452 ecr 4294935370], length 0
05:34:16.281157 IP 10.101.0.13.41531 > 10.101.99.5.3260: Flags [P.], seq 5376:5424, ack 54913, win 514, options [nop,nop,TS val 1732452 ecr 4294935370], length 48

05:34:16.281190 IP 10.101.99.5.3260 > 10.101.0.13.41531: Flags [P.], seq 54913:54961, ack 5424, win 235, options [nop,nop,TS val 4294935370 ecr 1732452], length 48
05:34:16.281208 IP 10.101.99.5.3260 > 10.101.0.13.41531: Flags [P.], seq 54961:55473, ack 5424, win 235, options [nop,nop,TS val 4294935370 ecr 1732452], length 512

05:34:16.281337 IP 10.101.0.13.41531 > 10.101.99.5.3260: Flags [.], ack 55473, win 514, options [nop,nop,TS val 1732452 ecr 4294935370], length 0
05:34:16.281390 IP 10.101.0.13.41531 > 10.101.99.5.3260: Flags [P.], seq 5424:5472, ack 55473, win 514, options [nop,nop,TS val 1732452 ecr 4294935370], length 48

05:34:16.281423 IP 10.101.99.5.3260 > 10.101.0.13.41531: Flags [P.], seq 55473:55521, ack 5472, win 235, options [nop,nop,TS val 4294935370 ecr 1732452], length 48
05:34:16.281440 IP 10.101.99.5.3260 > 10.101.0.13.41531: Flags [P.], seq 55521:56033, ack 5472, win 235, options [nop,nop,TS val 4294935370 ecr 1732452], length 512



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