Re: [RFC][PATCH] TTY flip buffer SMP changes

[Paul Fulghum]

On Fri, 2004-10-08 at 01:26, Theodore Ts'o wrote:
> Even if kmalloc() isn't as fast using two ring buffers which we flip
> back and forth, CPU's have gotten a lot faster since when I
> implemented the flip buffers some 12 years ago (i.e., 8 Moore law's
> doublings ago).

The sk_buff solution does look attractive,
particularly for high data rates.

It does seem to carry serious overhead (in relation
to ring buffers) for devices with small FIFOs.

At 115200bps, I saw the 16550 driver accumulate
~8 bytes per interrupt. Using 2 sk_buffs per interrupt
means 256 sk_buff allocations to push 1KiB (71ms) of data
to the line discipline. This amounts to ~3600 sk_buff
allocations per second at 115200bps.

-- 
Paul Fulghum
paulkf@xxxxxxxxxxxxx

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