Question about memcpy

[valdis.kletnieks at vt.edu]

On Fri, 13 Jul 2018 11:02:13 +0800, bing zhu said:

> I‘m trying to write a simple fs in user space,if memcpy is slower than
> kernel , i think it's unfair,as for only cpu for my task,
> it's a bit of arbitrary ，i just want my task not interrupted during a
> specific time is that possible ?

Not getting interrupted is an *entirely* different issue than making memcpy fast.

Note that in general, systems code should be able to deal with interruptions
during most parts of the code, and locking used and disabling pre-emption for
sections of code that can't deal with being interrupted.  Remember that if your
filesystem code turns off interrupts for long enough, you can start losing
things like I/O completions.  Fortunately for those who write systems code,
the vast majority of interrupts are totally transparent to the vast majority
of the kernel code.

And if you're doing a file system in userspace, you're going to fail to notice
hundreds or even thousands of interrupts happening. If you don't believe me,
'cat /proc/interrupts', and realize that userspace didn't notice *any* of them
happening.

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