lkml.org 
[lkml]   [2012]   [May]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb
    From
    Date
    On Thu, 2012-05-17 at 18:44 +0200, Peter Zijlstra wrote:
    >
    > So the RCU code can from ppc in commit
    > 267239116987d64850ad2037d8e0f3071dc3b5ce, which has similar behaviour.
    > Also I suspect the mm_users < 2 test will be incorrect for ARM since
    > even the one user can be concurrent with your speculation engine.
    >
    >
    Right, last mail, I promise, I've confused myself enough already! :-)

    OK, so ppc/sparc are special (forgot all about s390) I think by the time
    they are done with unmap_page_range() their hardware hash-tables are
    empty and nobody but software page-table walkers will still access the
    linux page tables.

    So when we do free_pgtables() to clean up the actual page-tables.
    Power/Sparc need to RCU free this to allow concurrent software
    page-table walkers like gup_fast.

    Thus I don't think they need to tlb flush again because their hardware
    doesn't actually walk the link page-tables, it walks hash-tables, which
    by this time are empty.

    Now if x86/Xen were to use this, it would indeed also need to TLB flush
    when freeing the page-tables, since its hardware walkers do indeed
    traverse these pages and we need to sync against them.

    So my first patch in the tlb-unify tree is actually buggy.

    Humm,. what to do adding a tlb flush in there might slow down ppc/sparc
    unnecessarily.. dave/ben? I guess we need more knobs :-(


    Now its quite possible I've utterly confused myself and everybody
    reading, apologies for that, I shall rest and purge all from memory and
    start over before commenting more..


    \
     
     \ /
      Last update: 2012-05-17 19:41    [W:3.222 / U:0.496 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site