Zack's Kernel News

Zack's Kernel News

Article from Issue 187/2016
Author(s):

Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.

Speeding Up Futexes…Maybe

Thomas Gleixner pointed out that the kernel's 'futex' locks used a global hash value to keep track of state changes, but that the hash values were not guaranteed to be unique. The kernel could handle these collisions, but it would slow things down. He posted a patch to provide a reference counting mechanism to allow threads to guarantee no hash collisions. He said, "this creates a futex private state that avoids hash collisions and on NUMA systems also cross-node memory accesses."

To make use of the mechanism, he said, "each thread has to attach to the futex before any other operations on that futex." He explained the usage of the sys_futex() call to increment and decrement the futex reference count.

Thomas added that, although the user interface could be simplified by having threads automatically attach to the futex, he didn't want to implement it that way. Apart from increasing memory usage, the futex attachment code would have its own performance issues if all threads on the system made use of it. As long as it was used only by threads that actually needed to avoid those hash collisions – in other words, for real-time software – the code would provide a measurable performance increase.

[...]

Use Express-Checkout link below to read the full article (PDF).

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

SINGLE ISSUES
 
SUBSCRIPTIONS
 
TABLET & SMARTPHONE APPS
Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Kernel News

    Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.

  • Kernel News

    Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.

  • Kernel News

    Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.

  • Kernel News

    Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.

  • Kernel News

    Zack Brown reports on container-aware cgroups, a different type of RAM chip on a single system, new SARA security framework, and improving GPIO interrupt handling.

comments powered by Disqus
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters

Support Our Work

Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

Learn More

News