lkml.org 
[lkml]   [2012]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH RFC tip/core/rcu 17/41] rcu: Remove single-rcu_node optimization in rcu_start_gp()
    On Wed, Feb 01, 2012 at 06:13:14PM -0800, Josh Triplett wrote:
    > On Wed, Feb 01, 2012 at 11:41:35AM -0800, Paul E. McKenney wrote:
    > > The grace-period initialization sequence in rcu_start_gp() has a special
    > > case for systems where the rcu_node tree is a single rcu_node structure.
    > > This made sense some years ago when systems were smaller and up to 64
    > > CPUs could share a single rcu_node structure, but now that large systems
    > > are common and a given leaf rcu_node structure can support only 16 CPUs
    > > (due to lock contention on the rcu_node's ->lock field), this optimization
    > > is almost never taken. And even the small mobile platforms that might
    > > make use of it might rather have the kernel text reduction.
    > >
    > > Therefore, this commit removes the check for single-rcu_node trees.
    >
    > This optimization would continue to work on laptops for a while longer.
    > :)

    How many more months? ;-)

    > That said, I do agree that reducing code size and complexity seems
    > preferable. If someone wants an optimization like this, they'd probably
    > do better to compile RCU with a low compile-time limit on the number of
    > CPUs, which would at least theoretically allow the compiler to get
    > similar results through optimization. (I don't know if that works in
    > practice with the current code structure and the current intelligence of
    > GCC.)
    >
    > Reviewed-by: Josh Triplett <josh@joshtriplett.org>

    Thank you for all your reviews -- as always, very helpful!!!

    Thanx, Paul



    \
     
     \ /
      Last update: 2012-02-02 18:55    [W:4.268 / U:0.280 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site