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Cache trashing

Cache trashing

Posted Jan 14, 2005 5:06 UTC (Fri) by goaty (guest, #17783)
In reply to: Faster page faulting through prezeroing by huaz
Parent article: Faster page faulting through prezeroing

I think the idea is not so much to prevent cache trashing, which is after all inevitable, but to make it happen less often. If kswapd pre-zeroes a big sack of pages, then that's more efficient than zeroing them one at a time. And of course if the hardware can be persuaded to zero chunks of RAM without touching the processor cache, then you've got a huge win.

In a couple of years it might even be possible to buy a PCI Express "/dev/null" card to accelerate your server.


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Cache trashing

Posted Feb 12, 2008 0:31 UTC (Tue) by goaty (guest, #17783) [Link]

2+ years ago, I wrote: In a couple of years it might even be possible to buy a PCI Express "/dev/null" card to accelerate your server.

Unfortunately, this did not happen. As someone pointed out in another thread, it's possible to persuade various DMA-capable hardware to act as a /dev/null device. For example, you can stick a page full of zeroes on the swap device and then get the IDE controller to DMA it to wherever its needed. Provided the drive's cache is larger than the page size, the performance should be acceptable.

The problem being that most of the devices on the system are already busy with their intended function, like reading and writing files, and cannot expend time in the frivolous pursuit of nullage.


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