From: Steven Rostedt <rostedt@goodmis.org>
To: Menglong Dong <menglong8.dong@gmail.com>
Cc: mhiramat@kernel.org, mark.rutland@arm.com,
mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org,
linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org,
Menglong Dong <dongml2@chinatelecom.cn>
Subject: Re: [PATCH bpf] ftrace: fix incorrect hash size in register_ftrace_direct()
Date: Sat, 12 Apr 2025 10:45:18 -0400 [thread overview]
Message-ID: <20250412104518.2b4598d3@batman.local.home> (raw)
In-Reply-To: <CADxym3bAXpqC3awWBTm+zc4Wn348=7cYVCN_+em=b5qPimUTYQ@mail.gmail.com>
On Sat, 12 Apr 2025 22:36:56 +0800
Menglong Dong <menglong8.dong@gmail.com> wrote:
> > Yeah, this seems to make more sense. And I'll send a V2
> > later.
> >
> > BTW, Should we still keep the "size = min(size, 32)" logic
>
> Oops, I mean "size = max(size, 32); size = fls(size);" here :/
>
> > to avoid the hash bits being too small, just like the origin
> > logic in "dup_hash"?
> >
If you have 5 functions, why do you need more that 5 buckets?
size = 5;
size = max(5, 32); // size = 32
size = fls(size); // size = 5
alloc_ftrace_hash(size);
size = 1 << size; // size = 32
hash->buckets = kcalloc(size, ...);
Now you have 32 buckets for 5 functions. Why waste the memory?
If you add more functions, the hash bucket size will get updated.
-- Steve
next prev parent reply other threads:[~2025-04-12 14:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-12 13:33 [PATCH bpf] ftrace: fix incorrect hash size in register_ftrace_direct() Menglong Dong
2025-04-12 14:09 ` Steven Rostedt
2025-04-12 14:32 ` Menglong Dong
2025-04-12 14:36 ` Menglong Dong
2025-04-12 14:45 ` Steven Rostedt [this message]
2025-04-13 1:32 ` Menglong Dong
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