On 5/27/25 8:21 AM, Jₑₙₛ Gustedt wrote:

Hello Carlos,

On Tue, 27 May 2025 07:30:09 -0400, Carlos O'Donell wrote:

quoted

quoted

This has several issues, the most severe beeing the word
`FUTEX_WAIT`.

- How can an operation that only does wakes, ever be equivalent to a
    wait?

My opinion is that the text is correct.

The operation can WAKE tasks.

The operation can also cause tasks to WAIT in a *different* queue.

No, it can make *other* threads wait in a different queue. The
`FUTEX_WAIT` call is to put the current thread on wait. So calling
this equivalent is really far fetched.

Sorry, I'm not sure what you're saying "No" to in this case.

I wrote that it can cause tasks to wait in a different queue, but you
wrote threads. Threads are really a userspace construct, while the
Linux kernel is really only aware tasks that have properties, so I
tend to call them tasks when speaking about the kernel tasks.

The text in question is parenthetical, and is correct for a val==0
API call, where zero waiters are woken, but for which up to val2
waiters are "moved" (atomic WAKE/WAIT into uaddr2).

While you call it "far fetched" is a parenthetical side comment
that is correct for the odd corner case of val==0?

-- 
Cheers,
Carlos.