[Dovecot] Dovecot I/O scheduling (all versions)

[Kyle Wheeler]

On Sunday, November  4 at 01:02 PM, quoth mikkel at euro123.dk:
> What I see is that if there is a peak in disk usage at the time of a 
> specific request that requests stalls. The saturation of disk I/O is 
> momentary but when it’s done (maybe after one or two seconds) 
> Dovecot still waits for its I/O operation instead of continuing as 
> soon as resources are available.

Unfortunately, that's probably an OS thing. It's a pain (though 
technically possible) for user programs like Dovecot to worry about 
I/O scheduling, so generally they do not: that is something that the 
OS handles. Dovecot, like virtually all user programs, simply asks the 
OS for the contents of the files it wants. When that happens, the 
state of the requesting program (Dovecot) changes from "running" to 
"blocked" while the OS services the request. Once the request is 
serviced, it is the OS's responsibility to return the requesting 
program to "runnable" status and begin scheduling it on the CPU again. 
There's very little that Dovecot (or any program) can do to improve 
the situation if the OS refuses to service I/O requests in a timely 
fashion.

~Kyle
-- 
You can not establish sound security, on borrowed money. You can not 
keep out of trouble, by spending more than you earn.
                                                    -- Abraham Lincoln
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