linux-kernel - Re: [patch 5/9] Add all the necessary structures to the vsyscall page

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Message-Id: <200702011217.42286.ak@suse.de>
Date:	Thu, 1 Feb 2007 12:17:42 +0100
From:	Andi Kleen <ak@...e.de>
To:	jbohac@...e.cz
Cc:	linux-kernel@...r.kernel.org, Vojtech Pavlik <vojtech@...e.cz>,
	ssouhlal@...ebsd.org, arjan@...radead.org, tglx@...utronix.de,
	johnstul@...ibm.com, zippel@...ux-m68k.org, andrea@...e.de
Subject: Re: [patch 5/9] Add all the necessary structures to the vsyscall page

On Thursday 01 February 2007 10:59, jbohac@...e.cz wrote:
>  struct vxtime_data {
> +	union {
> +		struct {
> +			u64 tsc_slope;		/* TSC to MT coefficient */
> +			u64 tsc_slope_avg;	/* average tsc_slope */
> +			u64 mt_base;		/* approximated MT at the last LAPIC tick */
> +			u64 mt_last;		/* MT at the last LAPIC tick */
> +			u64 tsc_last;		/* TSC at the last LAPIC tick */
> +			u64 last_mt_guess;	/* ensures monotonicity in temporary MT mode */
> +			char tsc_invalid;	/* don't trust the TSC now (frequency changing) */
> +		};
> +		char pad[64];	/* cacheline alignment */

Use some variant of __cacheline_aligned_in_smp

There are far better ways than to hardcode

> +	} cpu[NR_CPUS];

This can become very large with default NR_CPUS==128. I would prefer
a way that waste less space on smaller machines by only sizing the array
num_possible_cpus()

>  	long hpet_address;	/* HPET base address */
> -	int last;
> -	unsigned long last_tsc;
> -	long quot;
> -	long tsc_quot;
> +	u64 mt_q;		/* master timer to nsec quotient */
> +	u64 mt_wall;		/* MT ticks already covered by the jiffies */
> +	s64 ns_drift;		/* MT - xtime drift in the last tick in ns */

Might make sense to duplicate those to all per cpu datas, then they 
only need to acce

-Andi
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