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Date: Tue, 19 Nov 2024 17:17:53 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Cc: Borislav Petkov <bp@alien8.de>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Eduard Zingerman <eddyz87@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Yonghong Song <yonghong.song@linux.dev>,
	Mykola Lysenko <mykolal@fb.com>, x86@kernel.org,
	bpf@vger.kernel.org, Martin KaFai Lau <martin.lau@linux.dev>
Subject: Re: [PATCH bpf-next v7 1/4] bpf: add bpf_get_cpu_cycles kfunc
Message-ID: <20241119161753.GA28920@noisy.programming.kicks-ass.net>
References: <20241118185245.1065000-1-vadfed@meta.com>
 <20241118185245.1065000-2-vadfed@meta.com>
 <20241119111809.GB2328@noisy.programming.kicks-ass.net>
 <bade75b3-92d2-42e8-aede-f7a361b491a9@linux.dev>
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In-Reply-To: <bade75b3-92d2-42e8-aede-f7a361b491a9@linux.dev>

On Tue, Nov 19, 2024 at 06:29:09AM -0800, Vadim Fedorenko wrote:
> On 19/11/2024 03:18, Peter Zijlstra wrote:
> > On Mon, Nov 18, 2024 at 10:52:42AM -0800, Vadim Fedorenko wrote:
> > > @@ -2094,6 +2094,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
> > >   			if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
> > >   				int err;
> > > +				if (imm32 == BPF_CALL_IMM(bpf_get_cpu_cycles)) {
> > > +					if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC))
> > > +						EMIT3(0x0F, 0xAE, 0xE8);
> > > +					EMIT2(0x0F, 0x31);
> > > +					break;
> > > +				}
> > 
> > TSC != cycles. Naming is bad.
> 
> Any suggestions?
> 
> JIT for other architectures will come after this one is merged and some
> of them will be using cycles, so not too far away form the truth..

bpf_get_time_stamp() ?
bpf_get_counter() ?