lkml.org 
[lkml]   [2017]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 2/2] vfs: grab the lock instead of blocking in __fd_install during resizing
    On Wed, Oct 04, 2017 at 07:00:40AM -0700, Eric Dumazet wrote:
    > On Wed, Oct 4, 2017 at 6:55 AM, Matthew Wilcox <willy@infradead.org> wrote:
    > > Any chance you could review the patches from Sandhya that make this entire
    > > codepath obsolete?
    > >
    > > https://lkml.org/lkml/2017/4/29/20
    > >
    >
    > Hmm...
    >
    > 18 files changed, 578 insertions(+), 585 deletions(-)
    >
    > Frankly I need to be convinced with solid performance numbers before I
    > am taking a look at this series.

    I was hoping you'd help us get some solid performance numbers ... you
    seem to have workloads available to you that help find weaknesses in
    implementations.

    The number of lines inserted is a bit of a red herring. Over 100 are in
    the test suite (you surely aren't going to review those) and another ~300
    are adding enhancements to the IDR & radix tree that should be useful
    for other users (eg I think I have a way to speed up writing out dirty
    pages by using get_tag_batch()).

    > I do not believe an IDR will be faster than current implementation, so
    > I am not quite convinced at this moment.

    I don't think it should be significantly different in performance. Let's
    look at the layout of data for a typical bash shell (fds 0-2 and 255 open).

    Current implementation:

    files_struct -> fdt -> fd -> struct file

    IDR:

    files_struct -> radix node (shift 6) -> radix node (shift 0) -> struct file

    In either case, it's the same number of dependent loads. It'll start
    to look worse for the radix tree above 4096 open fds in a given process.

    \
     
     \ /
      Last update: 2017-10-04 17:00    [W:2.703 / U:0.000 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site