From: David Howells

Sent: 15 September 2023 12:23

David Laight [off-list ref] wrote:

quoted

quoted

quoted

Some measurements can be made using readv() and writev()
on /dev/zero and /dev/null.

Forget /dev/null; that doesn't actually engage any iteration code.  The same
for writing to /dev/zero.  Reading from /dev/zero does its own iteration thing
rather than using iterate_and_advance(), presumably because it checks for
signals and resched.

Using /dev/null does exercise the 'copy iov from user' code.

Ummm....  Not really:

I was thinking of import_iovec() - or whatever its current
name is.

That really needs a single structure that contains the iov_iter
and the cache[] (which the caller pretty much always allocates
in the same place).
Fiddling with that is ok until you find what io_uring does.
Then it all gets entirely horrid.

	David

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