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Thu, 16 Oct 2025 06:14:19 +0000 Message-ID: Date: Thu, 16 Oct 2025 08:14:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCHv2 4/4] nvme-multipath: add debugfs attribute for adaptive I/O policy stat To: Nilay Shroff , linux-nvme@lists.infradead.org Cc: kbusch@kernel.org, hch@lst.de, axboe@kernel.dk, dwagner@suse.de, gjoyce@ibm.com References: <20251009100608.1699550-1-nilay@linux.ibm.com> <20251009100608.1699550-5-nilay@linux.ibm.com> <359e3d8f-4db7-4430-8520-4fed9de4f48e@suse.de> <4faf672b-ad74-41dc-9518-bbb9af557544@linux.ibm.com> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <4faf672b-ad74-41dc-9518-bbb9af557544@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 148AA21EA4 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCPT_COUNT_SEVEN(0.00)[7]; MID_RHS_MATCH_FROM(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.de:email,suse.de:mid,suse.de:dkim] X-Rspamd-Action: no action X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251015_231424_783674_3C9220E6 X-CRM114-Status: GOOD ( 11.96 ) 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 10/15/25 08:19, Nilay Shroff wrote: > > > On 10/13/25 12:03 PM, Hannes Reinecke wrote: >> On 10/9/25 12:05, Nilay Shroff wrote: >>> This commit introduces a new debugfs attribute, "adaptive_stat", under >>> both per-path and head debugfs directories (defined under /sys/kernel/ >>> debug/block/). This attribute provides visibility into the internal >>> state of the adaptive I/O policy to aid in debugging and performance >>> analysis. >>> >>> For per-path entries, "adaptive_stat" reports the corresponding path >>> statistics such as I/O weight, selection count, processed samples, and >>> ignored samples. >>> >>> For head entries, it reports per-CPU statistics for each reachable path, >>> including I/O weight, path score, smoothed (EWMA) latency, selection >>> count, processed samples, and ignored samples. >>> >>> These additions enhance observability of the adaptive I/O path selection >>> behavior and help diagnose imbalance or instability in multipath >>> performance. >>> >>> Signed-off-by: Nilay Shroff >>> --- >>>   drivers/nvme/host/core.c      |   3 + >>>   drivers/nvme/host/debugfs.c   | 117 ++++++++++++++++++++++++++++++++++ >>>   drivers/nvme/host/multipath.c |   2 + >>>   3 files changed, 122 insertions(+) >>> >> Reviewed-by: Hannes Reinecke >> >> Might be an idea to have support for queue-depth in here, too. >> > Currently queue_depth and numa_nodes attributes are created under > sysfs, so do you meant to move those attributes from sysfs to > debugfs? > Yes. sysfs information can be perused by udev rules, and that assumes the information in there will not change without a 'CHANGE' uevent. So it's questionable whether volatile information like the queue depth or the round-robin path selection should be presented there. I'd rather have it moved into debugfs. But that might be personal preference. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich