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Wed, 5 Aug 2026 07:15:06 +0000 (GMT) Message-ID: <9c59f7d4-03f3-4d7f-b77a-fdbab9a82ce7@linux.ibm.com> Date: Wed, 5 Aug 2026 12:45:04 +0530 Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 10/17] preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS To: Boqun Feng Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Gary Guo , Alice Ryhl , Lyude Paul , Daniel Almeida , =?UTF-8?Q?Onur_=C3=96zkan?= , Miguel Ojeda , Danilo Krummrich , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org References: <20260804161447.84806-1-boqun@kernel.org> <20260804161447.84806-11-boqun@kernel.org> <2a9aec78-fe1b-49c9-884f-a59eb36c8905@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwODA1MDA1MSBTYWx0ZWRfXxolL4YAJ1PKJ ssVQiywsV7uZ+cYigvGkQDEkfKqjjIrRTNK/Y/AxPTDe4w1aSfHJYdFfbGLDoINWfsliKMw4vWN pZq8viOvb5jr8qMKTDtBsbT7ovd/YVk= X-Authority-Analysis: v=2.4 cv=I7VVgtgg c=1 sm=1 tr=0 ts=6a72e304 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=USvw5ZzSzfr2lKRvkucA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA1MDA1MSBTYWx0ZWRfX30H5BuJkrMg/ 4QEPBTN9BpGIm2zrAVQ11frDH4jp63W77iYlK6oQ/zNLJjA3z+Co5hKKFfFl+VgjqmsMOoyPw4G Ofmwda2GPRrWRQbDGocTiCm57m8WewLzR43tAvUmRXzanmMNC80pCsrDyxvIKNRUNAPaoYi3emO gwI7CDYg7GU7ycerI0KuFZZERrnFzmdENqaMlncx+69VlDCS9M0kgiuccbU2bcguTgwETmHVHRV wMLnhN71pI8WiIiwLCL91Xw7inbe8SsrxD5D/ugjrVWdRd2MHbp+FTB/nPaD9bxJ5+BL7Wt2wxv ZNDNup4F0kmaCTDjxx0c8a8G0ImcgV1ZW6RDVKmoyYbx7RWT+qoh4/8YNAHOczU9LrjG5zdhSiW z8PXTuSAZjynfiJsoMHPsFQLpitvDP32XImyOibjdCtGDLTKFFOz9l+GiRg4GpzpGqDslnP/1u3 +sXRPR3B04qbQIrXWMg== X-Proofpoint-ORIG-GUID: EKXDyEEUVGvdlrVvYoh4P1u4MyRtEcGr X-Proofpoint-GUID: G5YWBUl91z4LQHD4nGBY_EwVowML7QUI X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-05_02,2026-08-04_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 impostorscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 malwarescore=0 adultscore=0 lowpriorityscore=0 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608050051 Hi Boqun. >> nit: This limit is because to have the same behavior as other case when >> NMI_BITS=4 right? >> It is not easy to infer that from comment. >> > > It's sort of design by implementation IIUC, previously because of > NMI_BITS=4, we could only support nesting level being 15. And here we > just want to keep the same behavior here. That I understood. > > If your question is why 15 was a good number before this change, I guess > would be it's just a number that is neither too big or too small. Its more about below comment. Something like below is better? /* NMI nesting is represented in 4 bits. */ > >>> + /* Maximum NMI nesting is 15. */ \ >>> + BUG_ON(__this_cpu_read(nmi_nesting) >= 15); \ >>> + __this_cpu_inc(nmi_nesting); \ >>> + preempt_count_set(preempt_count() | NMI_MASK); \