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SubjectRe: [PATCH 0/3] Transition /proc/cpuinfo -> sysfs
On Wed, Aug 11, 2004 at 04:42:45PM -0700, Deepak Saxena wrote:

> > For x86 at least, this can be entirely decoded in userspace using
> > the /dev/cpu/x/cpuid interface. See x86info for example of this.
> >
> > > - Instead of dumping the "flags" field, should we just dump cpu
> > > registers as hex strings and let the user decode (as the comment
> > > for the x86_cap_flags implies.
> >
> > ditto.
>
> OK, just saw that code now and my reponse is to remove that
> interface in the long-term and move cpuid into sysfs (and not
> export all the cache info separately).

but why? it's totally pointless when the same info can be obtained
from userspace without the bloat.

> In theory we don't even
> need the xxx_bug fields as those can be determined from looking
> at CPU binary data.

not all of them you can't iirc.

> > As these require arch specific parsers anyway, I don't think it makes
> > too much sense making a kernel abstraction trying to make them all
> > look 'the same', and if it can be done in userspace, why bother ?
>
> If it is all done in userspace, then just having the raw binary
> data available via sysfs w/o kernel parsing is probably best.

the raw binary is already available. in /dev/cpu/x/cpuid
I repeat, duplicating this in sysfs is utterly pointless other than
to bloat the kernels runtime memory usage.

> > The only other concern I have is the further expansion of sysfs with
> > no particular gain over what we currently have. The sysfs variant
> > *will* use more unreclaimable RAM than the proc version.
>
> Agreed, but that hasn't kept other data such as PCI and partition
> information from moving into sysfs.

So because one subsystem decides to do it, every other should follow
lemming-like ?

> > /proc/cpuinfo has done well enough for us for quite a number of years
> > now, what makes it so urgent to kill it now that sysfs is the
> > virtual-fs-de-jour ?
>
> Consitency in userspace interface.

sorry, but I think that argument is total crap. Any userspace tool needing
this info will still need to support the /dev/cpu/ interfaces if they want to
also run on 2.2 / 2.4 kernels. Likewise, anything using /proc/cpuinfo.
Ripping this out does nothing useful that I see other than cause headache
for userspace by having yet another interface to support.

> My understanding is that goal is to
> make /proc slowly return to it's original purpose (process-information)
> and move other data out into sysfs.

I don't think thats a realistic goal. It'll take years just to migrate the
in-kernel stuff, and there's god alone knows how much out-of-tree code doing
the same, plus the add-ons from various vendor kernels etc so I doubt it'll
ever be the process-only utopia you envision.

Changing userspace interfaces on a whim just causes pain for those
that use them, especially when there is nothing wrong with the existing
interfaces.

Dave

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