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SubjectRe: [PATCH -v4] x86: MCE: Re-implement MCE log ring buffer as per-CPU ring buffer
Huang Ying wrote:
> Re-implement MCE log ring buffer as per-CPU ring buffer for better
> scalability. Basic design is as follow:

That would be great. This should be in .31, I think.

Some minor points:

> struct mce_log {
> - char signature[12]; /* "MACHINECHECK" */
> + char signature[12]; /* "MACHINECHEC2" */
> unsigned len; /* = MCE_LOG_LEN */
> - unsigned next;
> unsigned flags;
> unsigned pad0;
> - struct mce entry[MCE_LOG_LEN];
> + struct mce_log_cpu *mcelog_cpus;
> };

What is this *mcelog_cpus to be used for?
It seems it will point one of per-CPU buffers (maybe cpu#0's buffer)
if I have read the following mce_log_init() correctly.

> @@ -642,6 +669,16 @@ static int mce_cap_init(void)
> return 0;
> }
>
> +/*
> + * Initialize MCE per-CPU log buffer
> + */
> +static __cpuinit void mce_log_init(void)
> +{
> + if (mcelog.mcelog_cpus)
> + return;
> + mcelog.mcelog_cpus = &per_cpu_var(mce_log_cpus);
> +}
> +
> static void mce_init(void)
> {
> mce_banks_t all_banks;


Next,

> +static int mce_empty_cpu(struct mce_log_cpu *mcelog_cpu)
> +{
> + int head, tail;
> + head = mcelog_cpu->head;
> + tail = mcelog_cpu->tail;
> + return head == tail;
> +}

Are there any race condition?
Why we cannot have "return (mcelog_cpu->head == mcelog_cpu->tail);"?


Last,

> +static ssize_t mce_read(struct file *filp, char __user *inubuf, size_t usize,
> + loff_t *off)
> +{
> + char __user *ubuf = inubuf;
> + struct mce_log_cpu *mcelog_cpu;
> + int cpu, new_mce, err = 0;
> + static DEFINE_MUTEX(mce_read_mutex);
> +
(snip)
> + return err ? : ubuf - inubuf;
> }

It would be better to put "static DEFINE_MUTEX(mce_read_mutex)" to outside of
the function.

And it looks work, but I'd prefer:
return err ? err : ubuf - inubuf;


Overall it looks good.
Unfortunately there were updates on tip/mce3 so I could not apply this
patch on the top of the branch. I'd appreciate it if you could rebase
this patch again.


Thanks,
H.Seto



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