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From: "Xu, Yanfei" <yanfei.xu@windriver.com>
To: Will Deacon <will@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>
Cc: ast@kernel.org, zlim.lnx@gmail.com, catalin.marinas@arm.com,
	andrii@kernel.org, kafai@fb.com, songliubraving@fb.com,
	yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] bpf: avoid unnecessary IPI in bpf_flush_icache
Date: Wed, 2 Jun 2021 19:26:03 +0800	[thread overview]
Message-ID: <7637dcdf-12b4-2861-3c76-f8a8e240a05e@windriver.com> (raw)
In-Reply-To: <20210601174114.GA29130@willie-the-truck>



On 6/2/21 1:41 AM, Will Deacon wrote:
> [Please note: This e-mail is from an EXTERNAL e-mail address]
> 
> On Tue, Jun 01, 2021 at 07:20:04PM +0200, Daniel Borkmann wrote:
>> On 6/1/21 5:06 PM, Yanfei Xu wrote:
>>> It's no need to trigger IPI for keeping pipeline fresh in bpf case.
>>
>> This needs a more concrete explanation/analysis on "why it is safe" to do so
>> rather than just saying that it is not needed.
> 
> Agreed. You need to show how the executing thread ends up going through a
> context synchronizing operation before jumping to the generated code if
> the IPI here is removed.

This patch came out with I looked through ftrace codes. Ftrace modify
the text code and don't send IPI in aarch64_insn_patch_text_nosync(). I
mistakenly thought the bpf is same with ftrace.

But now I'm still not sure why the ftrace don't need the IPI to go
through context synchronizing, maybe the worst situation is omit a
tracing event?

Thanks,
Yanfei

> 
> Will
> 

WARNING: multiple messages have this Message-ID (diff)
From: "Xu, Yanfei" <yanfei.xu@windriver.com>
To: Will Deacon <will@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>
Cc: ast@kernel.org, zlim.lnx@gmail.com, catalin.marinas@arm.com,
	andrii@kernel.org, kafai@fb.com, songliubraving@fb.com,
	yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] bpf: avoid unnecessary IPI in bpf_flush_icache
Date: Wed, 2 Jun 2021 19:26:03 +0800	[thread overview]
Message-ID: <7637dcdf-12b4-2861-3c76-f8a8e240a05e@windriver.com> (raw)
In-Reply-To: <20210601174114.GA29130@willie-the-truck>



On 6/2/21 1:41 AM, Will Deacon wrote:
> [Please note: This e-mail is from an EXTERNAL e-mail address]
> 
> On Tue, Jun 01, 2021 at 07:20:04PM +0200, Daniel Borkmann wrote:
>> On 6/1/21 5:06 PM, Yanfei Xu wrote:
>>> It's no need to trigger IPI for keeping pipeline fresh in bpf case.
>>
>> This needs a more concrete explanation/analysis on "why it is safe" to do so
>> rather than just saying that it is not needed.
> 
> Agreed. You need to show how the executing thread ends up going through a
> context synchronizing operation before jumping to the generated code if
> the IPI here is removed.

This patch came out with I looked through ftrace codes. Ftrace modify
the text code and don't send IPI in aarch64_insn_patch_text_nosync(). I
mistakenly thought the bpf is same with ftrace.

But now I'm still not sure why the ftrace don't need the IPI to go
through context synchronizing, maybe the worst situation is omit a
tracing event?

Thanks,
Yanfei

> 
> Will
> 

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-06-02 11:27 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-01 15:06 [PATCH 0/1] bpf: avoid unnecessary IPI in bpf_flush_icache Yanfei Xu
2021-06-01 15:06 ` Yanfei Xu
2021-06-01 15:06 ` [PATCH 1/1] " Yanfei Xu
2021-06-01 15:06   ` Yanfei Xu
2021-06-01 17:20   ` Daniel Borkmann
2021-06-01 17:20     ` Daniel Borkmann
2021-06-01 17:41     ` Will Deacon
2021-06-01 17:41       ` Will Deacon
2021-06-02 11:26       ` Xu, Yanfei [this message]
2021-06-02 11:26         ` Xu, Yanfei
2021-06-02 17:26         ` Will Deacon
2021-06-02 17:26           ` Will Deacon
2021-06-03 10:29           ` Xu, Yanfei
2021-06-03 10:29             ` Xu, Yanfei

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