On Thu, 2011-05-19 at 20:21 -0500, Eric Van Hensbergen wrote:

On Thu, May 19, 2011 at 7:39 PM, Benjamin Herrenschmidt
[off-list ref] wrote:

quoted

On Wed, 2011-05-18 at 16:24 -0500, Eric Van Hensbergen wrote:

quoted

BG/P maps firmware with an early TLB

That's a bit gross. How often do you call that firmware in practice ?
Aren't you better off instead inserting a TLB entry for it when you call
it instead ? A simple tlbsx. + tlbwe sequence would do. That would free
up a TLB entry for normal use.

Well, it depends on who you talk to.  The production software BG/P
guys use the firmware constantly, its the primary interface to the networks, the console,
and the management software which runs the machine.

Yuck.

As such the IO Node guys, the Compute Node Kernel guys and the
ZeptoOS guys use it quite a bit.  The kittyhawk guys on the other hand
barely use it at all, in fact I believe they do all the interaction with
it during uboot and then shut it off.

I would prefer that approach.

IIRC, the sticky question is RAS support, there are certain things it
wants to jump to firmware to deal with and expects things to be mapped
an pinned into memory.

Furthermore, I think it may make assumptions about where in the TLB the
mappings are.  

This is gross, especially on a system with only 64 SW loaded TLB
entries :-(

Since the kittyhawk guys
obviously ignore this by shutting it down, its not clear just how
important this is.  I'm game to
try the dynamic mapping as you suggest if you would prefer it.

I would yes, we can sort things out later for RAS.

Its worth mentioning that I believe with BG/Q, the plan is to rely on
the firmware even more extensively, but I haven't looked at any of the code yet to verify
whether or not this is true.

This is tantamount to linking a binary blob with the kernel ... it's a
fine line. At some point we might refuse the patches if they go too far
in that direction.

Cheers,
Ben.

     -eric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/