Re: [RFD w/info-PATCH] device arguments from lookup, partion code

Alexander Viro
2001-05-21T21:51:31Z

On Mon, 21 May 2001, Alan Cox wrote:

> > Which, BTW, is a wonderful reason for having multiple channels. Instead
> > of write(fd, "critical_command", 8); read(fd,....); you read from the right fd.
> > Opened before you enter the hotspot. Less overhead than ioctl() would
> > have...
>
> The ioctl is one syscall, the read/write pair are two. Im not sure that ioctl
> is going to be more overhead there. In the video4linux case the high overhead
> is acking frames received by mmap so might conceivably be considered one way

Sure. But we have to do two syscalls only if ioctl has both in- and out-
arguments that way. Moreover, we are talking about non-trivial in- arguments.
How many of these are in hotspots?