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Mon, 3 Aug 2026 12:42:19 +0000 (GMT) Date: Mon, 3 Aug 2026 14:42:18 +0200 From: Heiko Carstens To: Peter Zijlstra Cc: Boqun Feng , Ingo Molnar , Will Deacon , Waiman Long , Gary Guo , Alice Ryhl , Lyude Paul , Daniel Almeida , Onur =?iso-8859-1?Q?=D6zkan?= , Miguel Ojeda , Danilo Krummrich , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH 12/24] s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS Message-ID: <20260803124218.14792D9d-hca@linux.ibm.com> References: <20260731203031.13679-1-boqun@kernel.org> <20260731203031.13679-13-boqun@kernel.org> <20260803114032.GC687043@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260803114032.GC687043@noisy.programming.kicks-ass.net> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwODAzMDExMCBTYWx0ZWRfX6qvSVzlZ+Eyo zZs9svSabCiTxRnddEc8R2/aNIM03mhJiQNBm1GJh8iSsWw9ghc9bHZPPHbuhoWNnrBBowaMOWo OJdsXze8M4FUpaHXEIADVh6e+ZdQmS8= X-Authority-Analysis: v=2.4 cv=I7VVgtgg c=1 sm=1 tr=0 ts=6a708caf cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=kj9zAlcOel0A:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=csveCD0TJrq5keC42VAA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODAzMDExMCBTYWx0ZWRfXya3Tgv7of0Ij HOkc2wTvQVnzwuzfss9m6sxJvq6nJ5OaQ2qZNYPK+R1JKCd6sPfzVH16X7CR0gJsytfJyVIK2sb q93NLICXeVpxXJbQxFisemxh+2ZQe0aUnkqt7phsijC15IujgduFUcDKi6mue6lVUetqST3ULoG dB6dLqf/9ex8xVSTgb21tEXrvuH4pwRLbRa4kF/KQXKEeidr1AlURm14F3lhdIDq6D2uKV9jcrn SIm9q3W5JsNPpb2vKOjZ+bgNFrYcJo0LofQgb5DouFXDAiEN1nqd/CIR+XJKzrQsu7XPFGlA7Qp 8IykrwsJwsV9uj/JbzHtDNDZwcdobSBjycaXyJ6xaUOLHmemyT8w8/mzv77LA8pt0C7yIf2dXqx blfNe6IMT/AvKp7pV+/IqqQU0pvGIxTDqsjkH88sK7Ru8nZajrumSGg/EAfOCYnxZR0HM3N8nYy LvxLEEY/auxJojweysA== X-Proofpoint-ORIG-GUID: iQtphIMzdyn36CQrAuvIMeg3nnYM3N_u X-Proofpoint-GUID: KOh4Q5_5sk-g9411JdzStURiIJhf4W2A 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=2026-08-03_03,2026-07-30_01,2025-10-01_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-2608030110 On Mon, Aug 03, 2026 at 01:40:32PM +0200, Peter Zijlstra wrote: > On Fri, Jul 31, 2026 at 01:30:13PM -0700, Boqun Feng wrote: > > > @@ -26,25 +23,25 @@ > > */ > > static __always_inline int preempt_count(void) > > { > > - unsigned long lc_preempt, count; > > + unsigned long lc_preempt; > > + int count; > > > > - BUILD_BUG_ON(sizeof_field(struct lowcore, preempt_count) != sizeof(int)); > > - lc_preempt = offsetof(struct lowcore, preempt_count); > > + lc_preempt = offsetof(struct lowcore, preempt.count); > > /* READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED */ > > If I'm not mistaken, this comment is no longer accurate, since > NEED_RESCHED lives in the high word and you're only loading the low > word. True. Something like /* READ_ONCE(get_lowcore()->preempt.count) (without PREEMPT_NEED_RESCHED) */ might be better. > > asm_inline( > > - ALTERNATIVE("llgt %[count],%[offzero](%%r0)\n", > > - "llgt %[count],%[offalt](%%r0)\n", > > + ALTERNATIVE("ly %[count],%[offzero](%%r0)\n", > > + "ly %[count],%[offalt](%%r0)\n", > > ALT_FEATURE(MFEATURE_LOWCORE)) > > : [count] "=d" (count) > > : [offzero] "i" (lc_preempt), > > [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS), > > - "m" (((struct lowcore *)0)->preempt_count)); > > + "m" (((struct lowcore *)0)->preempt.count)); > > return count; > > }