Re: Make pipe data structure be a circular list of pages, rather than

From: Linus Torvalds (torvalds_at_osdl.org)
Date: 01/08/05

  • Next message: Adrian Bunk: "[2.6 patch] fs/ncpfs/ncplib_kernel.c: make a function static" 
    Date:	Sat, 8 Jan 2005 13:51:46 -0800 (PST)
To: Lee Revell <rlrevell@joe-job.com>

    On Sat, 8 Jan 2005, Lee Revell wrote:
    >
    > Many latency critical apps use (tmpfs mounted) FIFO's for IPC; the Linux
    > FIFO being one of the fastest known IPC mechanisms. Each client in the
    > JACK (http://jackit.sf.net) graph wakes the next one by writing a single
    > byte to a FIFO. Ardour's GUI, control, and audio threads interact via a
    > similar mechanism. How would you expect this change to impact the inter
    > thread wakeup latency? It's confusing when people say "performance",
    > meaning "increased throughput albeit with more latency". For many
    > people that's a regression.

    I posted the performance numbers in the thread already, and with every
    single throughput number I also talked abotu what the latency difference
    was. So quite frankly, if you were confused, I suspect it was because you
    didn't read them. Tssk, tssk.

    Short and sweet: the latency changes are in the noise for SMP, but can be
    seen on UP. I'll look at it a bit more: since I had to add the coalescing
    code anyway, I might also decide to re-use a buffer page rather than free
    it immediately, since that may help latency for small writes.

                    Linus
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  • Next message: Adrian Bunk: "[2.6 patch] fs/ncpfs/ncplib_kernel.c: make a function static"

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