On Sun, 3 Jan 2021 16:32:07 -0800, Paul E. McKenney wrote: > On Sun, Jan 03, 2021 at 10:24:29AM -0800, Paul E. McKenney wrote: >> On Sun, Jan 03, 2021 at 01:12:40PM +0900, Akira Yokosawa wrote: [...] >>> >>> Hi Paul, >>> >>> Off topic, but smp_read_barrier_depends() as a kernel API >>> has been removed since Linux v5.9 [1]. >>> Now READ_ONCE() for Alpha uses mb() [2]. >>> >>> You might want to reflect these changes in perfbook before the >>> release of the Second Edition. >>> >>> [1]: merge commit https://git.kernel.org/linus/145ff1ec090d >>> ("Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux") >>> [2]: commit https://git.kernel.org/linus/d64628588515 >>> ("alpha: Override READ_ONCE() with barriered implementation") >> >> Good catch, thank you! We will of course need to retain mention of >> smp_read_barrier_depends() given that people will be using pre-v4.15 >> (to say nothing of pre-v5.9) kernels for some time, but the main code >> does need to reflect the current state of the Linux kernel. >> >> Perhaps in the third edition we should drop any and all references >> to DEC Alpha. It is no longer in any way special, at least from the >> perspective of core kernel code. ;-) >> >> I suppose that the counter-argument is that non-Linux-kernel code might >> still need to pay attention, so maybe DEC Alpha needs to stay until such >> time as C/C++ handle address and data dependencies. Worth some thought. > > In the meantime, how about like this? Looks reasonable to me. There is a footnote which now looks redundant. Please find a patch below (on top your change) to remove it. With my patch (or similar) applied, Reviewed-by: Akira Yokosawa <akiyks@xxxxxxxxx> Thanks, Akira > > Thanx, Paul [...] ------------------------------------------------------------------------ commit 7069136668105b6d4fd2d0c2ea4951d83f2c5424 Author: Akira Yokosawa <akiyks@xxxxxxxxx> Date: Mon Jan 4 12:25:22 2021 +0900 memorder: Remove redundant footnote Now that it becomes contextually obvious that this paragraph is talking on the pre-v4.15 READ_ONCE() of Alpha, the footnote can be removed. Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx> diff --git a/memorder/memorder.tex b/memorder/memorder.tex index 28c54967..a907025e 100644 --- a/memorder/memorder.tex +++ b/memorder/memorder.tex @@ -3940,10 +3940,7 @@ This \co{smp_wmb()} on \clnref{wmb} of this listing guarantees that the element initialization in \clnrefrange{init:b}{init:e} is executed before the element is added to the list on \clnref{add}, so that the lock-free search will work correctly. -That is, it makes this guarantee on all CPUs {\em except} Alpha.\footnote{ - But Linux kernel versions v4.15 and later cause \co{READ_ONCE()} - to emit a memory barrier on Alpha, so this discussion applies - only to older versions of the Linux kernel.} +That is, it makes this guarantee on all CPUs {\em except} Alpha. \end{fcvref} \begin{listing}[tbp]
