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SubjectRe: [RFC PATCH 1/3] tracing: Add support for logging data to uncached buffer
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On 8/16/2018 8:29 AM, Steven Rostedt wrote:
>
> Sorry for the late reply, I actually wrote this email over a week ago,
> but never hit send. And the email was pushed back behind other
> windows. :-/
>
>

Thanks for the review Steven.
And no problem on late reply, I was working on Will's comment about
instrumentation in arch code and was about to respin a v2 patch. I have
replied inline, let me know if any more corrections or improvements can
be done. I would also like if Kees or someone from pstore could comment
on patch 2.

> On Fri, 3 Aug 2018 19:58:42 +0530
> Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> wrote:
>
>> diff --git a/kernel/trace/trace_rtb.c b/kernel/trace/trace_rtb.c
>> new file mode 100644
>> index 000000000000..e8c24db71a2d
>> --- /dev/null
>> +++ b/kernel/trace/trace_rtb.c
>> @@ -0,0 +1,160 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2018 The Linux Foundation. All rights reserved.
>> + */
>> +#include <linux/atomic.h>
>> +#include <linux/dma-mapping.h>
>> +#include <linux/export.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/of_device.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/rtb.h>
>> +#include <linux/sched/clock.h>
>> +
>> +static struct platform_device *rtb_dev;
>> +static atomic_t rtb_idx;
>> +
>> +struct rtb_state {
>> + struct rtb_layout *rtb;
>> + phys_addr_t phys;
>> + unsigned int nentries;
>> + unsigned int size;
>> + int enabled;
>> +};
>> +
>> +static struct rtb_state rtb = {
>> + .enabled = 0,
>> +};
>
> No need for the initialization, you could just have:
>
> static struct rtb_state rtb;
>
> And it will be initialized to all zeros. Or did you do that to document
> that it is not enabled at boot?
>

I will correct it in v2. RTB will not be enabled until pstore is
registered since we use pstore for logs. I will add a comment above the
static declaration saying so.

>> +
>> +static int rtb_panic_notifier(struct notifier_block *this,
>> + unsigned long event, void *ptr)
>> +{
>> + rtb.enabled = 0;
>> + return NOTIFY_DONE;
>> +}
>> +
>> +static struct notifier_block rtb_panic_blk = {
>> + .notifier_call = rtb_panic_notifier,
>> + .priority = INT_MAX,
>> +};
>> +
>> +static void rtb_write_type(const char *log_type,
>> + struct rtb_layout *start)
>> +{
>> + start->log_type = log_type;
>> +}
>> +
>> +static void rtb_write_caller(u64 caller, struct rtb_layout *start)
>> +{
>> + start->caller = caller;
>> +}
>> +
>> +static void rtb_write_data(u64 data, struct rtb_layout *start)
>> +{
>> + start->data = data;
>> +}
>> +
>> +static void rtb_write_timestamp(struct rtb_layout *start)
>> +{
>> + start->timestamp = sched_clock();
>> +}
>
> Why have the above static functions? They are not very helpful, and
> appear to be actually confusing. They are used once.
>

Yes you are right, will remove those.

>> +
>> +static void uncached_logk_pc_idx(const char *log_type, u64 caller,
>> + u64 data, int idx)
>> +{
>> + struct rtb_layout *start;
>> +
>> + start = &rtb.rtb[idx & (rtb.nentries - 1)];
>> +
>> + rtb_write_type(log_type, start);
>> + rtb_write_caller(caller, start);
>> + rtb_write_data(data, start);
>> + rtb_write_timestamp(start);
>
> How is the above better than:
>
> start->log_type = log_type;
> start->caller = caller;
> start->data = data;
> start->timestamp = sched_clock();
>
> ??
>

Sure, will change it to above and post v2.

>> + /* Make sure data is written */
>> + mb();
>> +}
>> +
>> +static int rtb_get_idx(void)
>> +{
>> + int i, offset;
>> +
>> + i = atomic_inc_return(&rtb_idx);
>> + i--;
>> +
>> + /* Check if index has wrapped around */
>> + offset = (i & (rtb.nentries - 1)) -
>> + ((i - 1) & (rtb.nentries - 1));
>> + if (offset < 0) {
>> + i = atomic_inc_return(&rtb_idx);
>> + i--;
>> + }
>> +
>> + return i;
>> +}
>> +
>> +noinline void notrace uncached_logk(const char *log_type, void *data)
>
> BTW, all files in this directory have their functions notrace by
> default.
>

Oh I missed it. Will remove notrace.

- Sai Prakash

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