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definitions=2023-07-26_07,2023-07-26_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 spamscore=0 adultscore=0 phishscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2306200000 definitions=main-2307260147 X-Proofpoint-GUID: 5yqrGKdR8pR6NEqtKEvWVuDeGkPDY9wq X-Proofpoint-ORIG-GUID: 5yqrGKdR8pR6NEqtKEvWVuDeGkPDY9wq X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230726_093648_733507_C0BD7E62 X-CRM114-Status: GOOD ( 28.62 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 26/07/2023 10:40, Ming Lei wrote: Hi Ming, > blk_mq_alloc_tag_set() may override set->nr_hw_queues as 1 in case of kdump > kernel. This way causes trouble for driver, because blk-mq and driver see > different queue mapping. Especially the only online CPU may not be 1 for > kdump kernel, in which 'maxcpus=1' is passed from kernel command line, "the only online CPU may not be 1 for kdump kernel, in which 'maxcpus=1' ..." - this seems inconsistent with the cover letter, where we have "'maxcpus=1' just bring up one single cpu core during booting." > then driver may map hctx0 into one inactive real hw queue which cpu > affinity is 0(offline). > > The issue exists on all drivers which use managed irq and support > multiple hw queue. > > Prepare for fixing this kind of issue by applying the added helper, so > driver can take blk-mq max nr_hw_queues knowledge into account when > calculating io queues. Could you alternatively solve in blk_mq_pci_map_queues() by fixing the mappings in case of kdump to have all per-CPU mappings point at the HW queue associated with cpu0 (which I assume would be active)? It ain't pretty ... > > Signed-off-by: Ming Lei > --- > block/blk-mq.c | 16 ++++++++++++++++ > include/linux/blk-mq.h | 1 + > 2 files changed, 17 insertions(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index b04ff6f56926..617d6f849a7b 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -140,6 +140,22 @@ void blk_mq_freeze_queue_wait(struct request_queue *q) > } > EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait); > > +/* > + * Return the max supported nr_hw_queues for each hw queue type > + * > + * blk_mq_alloc_tag_set() may change nr_hw_queues for kdump kernel, so > + * driver has to take blk-mq max supported nr_hw_queues into account > + * when figuring out nr_hw_queues from hardware info, for avoiding > + * inconsistency between driver and blk-mq. > + */ > +unsigned int blk_mq_max_nr_hw_queues(void) > +{ > + if (is_kdump_kernel()) > + return 1; > + return nr_cpu_ids; > +} We rely on the driver having set->nr_hw_queues == 1 for kdump, right? If so, how about enforcing it then, like: --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -4426,7 +4426,8 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set) * 64 tags to prevent using too much memory. */ if (is_kdump_kernel()) { - set->nr_hw_queues = 1; + if (set->nr_hw_queues != 1) + return -EINVAL; set->nr_maps = 1; set->queue_depth = min(64U, set->queue_depth); } Thanks, John