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Message-ID: <AANLkTilSrX5PifVHlxMjTK-wo_viD8IS_1m1k-vPOlE3@mail.gmail.com> Date: Fri, 28 May 2010 13:38:53 -0700 From: Ivan Novick <novickivan@...il.com> To: netdev@...r.kernel.org Cc: Tim Heath <theath@...enplum.com> Subject: Choppy TCP send performance Hello, I am using RHEL5 and have 1 Gigabit NIC cards. When doing a loop sending 128 KB blocks of data using TCP. I am using system tap to debug the performance and finding that: 90% of the send calls take about 100 micro seconds and 10% of the send calls take about 10 miliseconds. The average send time is about 1 milisecond The 10% of the calls taking about 10 milliseconds seem to be correlated with "sk_stream_wait_memory" calls in the kernel. sk_stream_wait_memory seems to be called when the send buffer is full and the next send call does not complete until the send buffer utilization goes down from 4,194,304 bytes to 2,814,968 bytes. This implies that the send that blocks on a full send buffer will not complete until there is 1 meg of free space in the send buffer even though the send could be accepted into the OS with only 128KB of free space. Do you think I am misinterpreting this data or is there a way to even out the send calls so that they they are more even in duration: approx 1 milisecond per call. Is there a parameter to reduce how much space needs to be free in the send buffer before a blocking send call can complete from user space? Cheers, Ivan -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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