Linux-kernel mailing list archive 1998-50,: Re: mmap() is slower than read() on SCSI/IDE on 2.0 and 2.1

# Re: mmap() is slower than read() on SCSI/IDE on 2.0 and 2.1

Jay Nordwick (nordwick@scam.XCF.Berkeley.EDU)
Mon, 14 Dec 1998 05:05:34 -0800

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>read() does more prefetching than mmap() faults do, at least this was
>the story last time I was playing around in this area...
>
>Later,
>David S. Miller
>davem@dm.cobaltmicro.com
>

How about cluing in the VM to prefetch with madvise() ? How would this
effect performance?

As side questions:
- why would read() do more prefetching than mmap()?
- If read() caused prefetching of blocks, the when a page faulted in
from an mmap() mapping, why wouldn't this cause prefetching?
- When a binary executable image is mmap()ed to be run, wouldn't you want
to prefetch blocks of code and data -- what would be the difference
between this and the user mmap()ing in a file?

Just getting new to Linux kernel sources (coming from spare time FreeBSD
hacking) and would appreciate any useful source people can point me to.

Thanks,
-jay

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- Next message: Jes Sorensen: "Re: PATCH: Raw device IO for 2.1.131"
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- In reply to: David S. Miller: "Re: mmap() is slower than read() on SCSI/IDE on 2.0 and 2.1"
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