On Mon, Jan 04, 2021 at 12:56:25PM +0900, Akira Yokosawa wrote: > 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> Applied and pushed both, thank you! Thanx, Paul > 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] >
