<div dir="ltr">The point of async IO threads is mainly to improve latency, not throughput. If many processes try to do a lot of I/O simultaneously, you want to make sure that they are never forced to wait for a long time because one of them is doing an unusually large I/O operation. However, managing the async I/O threads adds a little bit of overhead. If you're running a program where the only thing that matters is the total time from start to finish, on a single machine, and you don't care about the order in which individual processes get to do their work, then async I/O will not be particularly useful and mainly adds overhead. For example, in typical escripts it's a good idea to put %%! +A0 on the second or third line of the file.<br><br>(Caveat: the OTP team have said that +A0 is not a regularly tested thing and you should probably not use it if uptime is important. For scripts, benchmarks etc., I see no reason to avoid it as long as you know what your tradeoffs are.)<br><br></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><br> /Richard</div></div>
<br><div class="gmail_quote">2016-09-15 16:27 GMT+02:00 Vans S <span dir="ltr"><<a href="mailto:vans_163@yahoo.com" target="_blank">vans_163@yahoo.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="color:#000;background-color:#fff;font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px"><div dir="ltr">Running the rebar3 test suite, ct, passing A0 to the VM args is consistently outperforming using any value of A above 0. The test suite does over 1m iops.<br><br>This should not be the be the case, is not the whole point of async threads to improve io throughput?<br><br><br>The test can be setup by doing:<br><br>install a package called time (apt-get install time)<br><br>git clone <a href="https://github.com/erlang/rebar3.git" target="_blank">https://github.com/<wbr>erlang/rebar3.git</a><br>rebar3 install local</div><div dir="ltr">export <span style="font-family:"Courier New";white-space:pre-wrap">REBAR3_ERL_ARGS="+A0 +K true"</span></div><div dir="ltr">time -v $(LOCAL_INSTALL_REBAR3_BIN) ct<br></div><div dir="ltr">export <span style="font-family:"Courier New";white-space:pre-wrap">REBAR3_ERL_ARGS="+A1 +K true"</span></div><div dir="ltr">time -v $(LOCAL_INSTALL_REBAR3_BIN) ct</div><div dir="ltr">export <span style="font-family:"Courier New";white-space:pre-wrap">REBAR3_ERL_ARGS="+A100 +K true"</span></div><div dir="ltr">time -v $(LOCAL_INSTALL_REBAR3_BIN) ct</div><div dir="ltr"><br>(rebar3 passes +sbtu as well)</div><div dir="ltr"><br></div><div dir="ltr">Here is an example of some results:</div><div><br></div><pre style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:11.9px;margin-top:0px;font-stretch:normal;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;border-radius:3px;color:rgb(51,51,51);margin-bottom:0px!important;background-color:rgb(247,247,247)"><code style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:11.9px;padding:0px;margin-top:0px;margin-bottom:0px;border-radius:3px;word-break:normal;white-space:pre-wrap;border:0px;display:inline;overflow:visible;line-height:inherit;word-wrap:normal;background:transparent">%A0
Command being timed: "/home/user/.cache/rebar3/bin/<wbr>rebar3 ct"
User time (seconds): 203.63
System time (seconds): 12.12
Percent of CPU this job got: 128%
Elapsed (wall clock) time (h:mm:ss or m:ss): 2:48.44
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 369744
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 2710315
Voluntary context switches: 215661
Involuntary context switches: 219472
Swaps: 0
File system inputs: 40
File system outputs: 1078936
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
%A1
Command being timed: "/home/user/.cache/rebar3/bin/<wbr>rebar3 ct"
User time (seconds): 221.73
System time (seconds): 17.73
Percent of CPU this job got: 134%
Elapsed (wall clock) time (h:mm:ss or m:ss): 2:57.55
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 418184
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 2704281
Voluntary context switches: 2307583
Involuntary context switches: 306797
Swaps: 0
File system inputs: 48
File system outputs: 1078928
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
%A100
Command being timed: "/home/user/.cache/rebar3/bin/<wbr>rebar3 ct"
User time (seconds): 223.26
System time (seconds): 18.20
Percent of CPU this job got: 133%
Elapsed (wall clock) time (h:mm:ss or m:ss): 3:01.20
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 385492
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 2651960
Voluntary context switches: 2392798
Involuntary context switches: 404162
Swaps: 0
File system inputs: 72
File system outputs: 1078936
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0</code></pre></div></div><br>______________________________<wbr>_________________<br>
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