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[66.29.187.52]) by mx.google.com with ESMTPSA id pa5sm8132598pdb.28.2015.01.09.16.27.02 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Jan 2015 16:27:03 -0800 (PST) Message-ID: <54B071DC.9000307@kernel.dk> Date: Fri, 09 Jan 2015 17:27:08 -0700 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Mike Snitzer References: <54ABAB80.70006@acm.org> <20150106160553.GB10224@redhat.com> <54AC0A39.90801@kernel.dk> <54AD0B63.3010505@acm.org> <20150109194955.GA32641@redhat.com> <54B042FE.2000205@kernel.dk> <54B043FC.8000902@kernel.dk> <20150109214015.GA1032@redhat.com> <54B04E94.3010403@kernel.dk> <20150109222543.GA1190@redhat.com> In-Reply-To: <20150109222543.GA1190@redhat.com> X-RedHat-Spam-Score: -2.034 (BAYES_00, DCC_REPUT_13_19, RCVD_IN_DNSWL_LOW, SPF_SOFTFAIL, URIBL_BLOCKED) 209.85.220.51 mail-pa0-f51.google.com 209.85.220.51 mail-pa0-f51.google.com X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 X-Scanned-By: MIMEDefang 2.68 on 10.5.110.21 X-loop: dm-devel@redhat.com Cc: Keith Busch , Christoph Hellwig , device-mapper development , Bart Van Assche , "Jun'ichi Nomura" Subject: Re: [dm-devel] blk-mq request allocation stalls [was: Re: [PATCH v3 0/8] dm: add request-based blk-mq support] X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk Reply-To: device-mapper development List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 01/09/2015 03:25 PM, Mike Snitzer wrote: > On Fri, Jan 09 2015 at 4:56pm -0500, > Jens Axboe wrote: > >> On 01/09/2015 02:40 PM, Mike Snitzer wrote: >>> On Fri, Jan 09 2015 at 4:11pm -0500, >>> Jens Axboe wrote: >>> >>>> >>>> Actually, try this one instead, it should be a bit more precise than >>>> the first. >>>> >>> >>> Thanks for the test patch. >>> >>> I'm still seeing failures that look wrong (last_tag=127 could be edge >>> condition not handled properly?): >>> >>> [ 14.254632] __bt_get: values before for loop: last_tag=127, index=3 >>> [ 14.255841] __bt_get: values after for loop: last_tag=64, index=2 >>> [ 14.257036] >>> [ 14.257036] bt_get: __bt_get() returned -1 >>> [ 14.258051] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 >>> [ 14.259246] nr_free=128, nr_reserved=0 >>> [ 14.259963] active_queues=0 >>> >>> [ 213.115997] __bt_get: values before for loop: last_tag=127, index=3 >>> [ 213.117115] __bt_get: values after for loop: last_tag=96, index=3 >>> [ 213.118200] >>> [ 213.118200] bt_get: __bt_get() returned -1 >>> [ 213.121593] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 >>> [ 213.123960] nr_free=128, nr_reserved=0 >>> [ 213.125880] active_queues=0 >>> >>> [ 239.158079] __bt_get: values before for loop: last_tag=8, index=0 >>> [ 239.160363] __bt_get: values after for loop: last_tag=0, index=0 >>> [ 239.162896] >>> [ 239.162896] bt_get: __bt_get() returned -1 >>> [ 239.166284] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 >>> [ 239.168623] nr_free=127, nr_reserved=0 >>> [ 239.170508] active_queues=0 >> >> Thanks for testing, can you try this one? > > Huh, at least now we're now seeing some nr_free=0... but the last 3 > failures below look unnecessary still. E.g. the last_tag=127 case > > [ 13.895265] __bt_get: values before for loop: last_tag=59, index=1 > [ 13.895265] __bt_get: values after for loop: last_tag=32, index=1 > [ 13.895266] > [ 13.895266] bt_get: __bt_get() returned -1 > [ 13.895267] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 > [ 13.895267] nr_free=0, nr_reserved=0 > [ 13.895268] active_queues=0 > > [ 13.895269] __bt_get: values before for loop: last_tag=0, index=0 > [ 13.895270] __bt_get: values after for loop: last_tag=0, index=0 > [ 13.895270] > [ 13.895270] bt_get: __bt_get() returned -1 > [ 13.895271] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 > [ 13.895272] nr_free=0, nr_reserved=0 > [ 13.895272] active_queues=0 > [ 13.895324] __bt_get: values before for loop: last_tag=0, index=0 > [ 13.895324] __bt_get: values after for loop: last_tag=0, index=0 > [ 13.895325] bt_get: __bt_get() _still_ returned -1 > [ 13.895325] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 > [ 13.895326] nr_free=0, nr_reserved=0 > [ 13.895326] active_queues=0 > > [ 18.931425] __bt_get: values before for loop: last_tag=127, index=3 > [ 18.933317] __bt_get: values after for loop: last_tag=0, index=0 > [ 18.935140] > [ 18.935140] bt_get: __bt_get() returned -1 > [ 18.936807] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 > [ 18.938772] nr_free=128, nr_reserved=0 > [ 18.939927] active_queues=0 > > [ 489.119597] __bt_get: values before for loop: last_tag=95, index=2 > [ 489.120621] __bt_get: values after for loop: last_tag=96, index=3 > [ 489.121624] > [ 489.121624] bt_get: __bt_get() returned -1 > [ 489.122532] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 > [ 489.123581] nr_free=128, nr_reserved=0 > [ 489.124206] active_queues=0 > > [ 494.705758] __bt_get: values before for loop: last_tag=127, index=3 > [ 494.707797] __bt_get: values after for loop: last_tag=0, index=0 > [ 494.709696] > [ 494.709696] bt_get: __bt_get() returned -1 > [ 494.712459] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5 > [ 494.714403] nr_free=128, nr_reserved=0 > [ 494.715955] active_queues=0 I sent out the half-done v3, unfortunately. Can you try this? Both the cases with substantial nr_free are at the end of an index. If this one doesn't solve it, I'll reproduce it myself to save the ping-pong effort :-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 60c9d4a93fe4..1ce031a56080 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -142,29 +142,29 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx, static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag) { - int tag, org_last_tag, end; - bool wrap = last_tag != 0; + int tag, org_last_tag = last_tag; - org_last_tag = last_tag; - end = bm->depth; - do { -restart: - tag = find_next_zero_bit(&bm->word, end, last_tag); - if (unlikely(tag >= end)) { + while (1) { + tag = find_next_zero_bit(&bm->word, bm->depth, last_tag); + if (unlikely(tag >= bm->depth)) { /* * We started with an offset, start from 0 to * exhaust the map. */ - if (wrap) { - wrap = false; - end = org_last_tag; - last_tag = 0; - goto restart; + if (org_last_tag) { + last_tag = org_last_tag = 0; + continue; } return -1; } + + if (!test_and_set_bit(tag, &bm->word)) + break; + last_tag = tag + 1; - } while (test_and_set_bit(tag, &bm->word)); + if (last_tag >= bm->depth - 1) + last_tag = 0; + } return tag; } @@ -199,9 +199,13 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt, goto done; } - last_tag = 0; - if (++index >= bt->map_nr) + index++; + last_tag = (index << bt->bits_per_word); + + if (index >= bt->map_nr) { index = 0; + last_tag = 0; + } } *tag_cache = 0;