linux-kernel - Re: [PATCH v2] percpu: improve percpu_alloc

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Message-ID: <30a47b4e-7c4b-cd2d-998d-cfaf8d12d342@openvz.org>
Date:   Wed, 11 May 2022 08:11:54 +0300
From:   Vasily Averin <vvs@...nvz.org>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org
Subject: Re: [PATCH v2] percpu: improve percpu_alloc_percpu event trace

On 5/11/22 05:33, Roman Gushchin wrote:
> On Fri, May 06, 2022 at 10:29:25PM +0300, Vasily Averin wrote:
>>  TRACE_EVENT(percpu_alloc_percpu,
>>  
>> -	TP_PROTO(bool reserved, bool is_atomic, size_t size,
>> -		 size_t align, void *base_addr, int off, void __percpu *ptr),
>> +	TP_PROTO(unsigned long call_site,
>> +		 bool reserved, bool is_atomic, size_t size,
>> +		 size_t align, void *base_addr, int off,
>> +		 void __percpu *ptr, size_t bytes_alloc, gfp_t gfp_flags),
> 
> Don't we want to preserve the order and add the call_site at the end?
> Trace events are not ABI, but if we don't have a strong reason to break it,
> I'd preserve the old order.

I checked recent trace patches and found that order changes is acceptable.

commit 8c39b8bc82aafcc8dd378bd79c76fac8e8a89c8d
Author: David Howells <dhowells@...hat.com>
Date:   Fri Jan 14 11:44:54 2022 +0000

    cachefiles: Make some tracepoint adjustments

-           TP_printk("o=%08x i=%lx e=%d",
-                     __entry->obj, __entry->ino, __entry->error)
+           TP_printk("o=%08x dB=%lx B=%lx e=%d",
+                     __entry->obj, __entry->dino, __entry->ino, __entry->error)

On the other hand I'm agree to keep old order by default.
that's why I added bytes_alloc and gfp_flags to end of output.
However I think call_site is an exception. In all cases found, 
call_site is output first.
For me personally it simplified output parsing.

So I would like to know Steven's position on this question.

Thank you,
	Vasily Averin