From: john stultz <johnstul@us.ibm.com>
Date: 25 Jan 2003 19:36:26 -0800
Now, since it looks like you don't want any references to arch specific
code, switching on cpu_has_tsc may not be the way to go. Maybe we need
some alternate abstraction which would return the proper value on the
right arch? That way there wouldn't be the need for the duplicated
implementations.
I definitely see this as a good opportunity to clean this stuff
up completely. And this can even be done without breaking any
platform.
My suggestion is, specifically, to:
1) create an asm/pkt_tstamp.h file that net/pkt_sched.h
includes
2) move the current PSCHED_JIFFIES and PSCHED_GETTIMEOFDAY
implementation into asm-generic/pkt_tstamp.h
3) "for i in include/asm-*/" create ${i}/pkt_tstamp.h which
simply says:
#ifndef _${i}_PKT_TSTAMP_H
#define _${i}_PKT_TSTAMP_H
#define PSCHED_CLOCK_SOURCE PSCHED_JIFFIES
#include <asm-generic/pkt_tstamp.h>
#endif /* _${i}_PKT_TSTAMP_H */
That is step 1, then x86 et al. can implement their own
PSCHED_CPU implementations as appropriate.
This would also be a good opportunity to clean up and fix
the comments currently present in pkt_sched.h, for example
those comments talk about fastgettimeofday which was killed
some time ago :-)
Afterwards, I'd like this asm/pkt_tstamp.h thing to allow
platforms to implement more efficient versions of the
do_gettimeofday(&skb->stamp) calls we make in net/core/dev.c
This would involve the following:
1) Add "typedef XXX skb_stamp_t" to asm/pkt_tstamp.h, use skb_stamp_t
for 'stamp' member of struct sk_buff in linux/skbuff.h
2) Add "skb_gettimeofday(skb, tvalp)" interface to asm/pkt_tstamp.h
It's purpose is to convert whatever skb_stamp_t is into a
struct timeval (which is stored in the 'tvalp' argument)
As above, default implementations go into asm-generic/pkt_tstamp.h
therefore not breaking any platforms.
This could all even be done safely in 2.4.x, and I would appreciate it
if whoever did this kind of work submitted to Alexey and myself
patches for both trees.
Alexey, what do you think about this?
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