From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-84.mta1.migadu.com [95.215.58.84]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 07957492E22 for ; Thu, 10 Sep 2026 12:58:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.84 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789045133; cv=none; b=iWG3NmUzL1T9pcCPNZPffHejGRBht8IJDM5V0yHtutVtorJ3MQkUF5uhU9iBvazoEoRhVwxE9p1TJjKDKE5m4Y7deVYO1P8EpRH1ob+lJsjBs0Iybs3HWPUXCBR00Z/fpWGBtWgu7EJchnInOJsI1umazZETDjnTCI2OpqeNl2w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789045133; c=relaxed/simple; bh=kuqHBkMBo3V9YxQhfmvAdSRAURGFEJi13xW6az8I9eQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=moWSt5WQqu4+raD6yBYTE4b1mJ1ViPOEKFa3ldjag5oZEZVysa+w1b7967QojGAfvoHwuTDRes6XNLAPCTUXnQUCYhm/XALJqWUx2KNVW1jN8uWZOp6WwNDr37itHNJ5T8VY+TB7Yw+FsmtiNMBowxgrOFH+gb0gENb3s0Q6CCQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=c949H3Q9; arc=none smtp.client-ip=95.215.58.84 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="c949H3Q9" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=kuqHBkMBo3V9YxQhfmvAdSRAURGFEJi13xW6az8I9eQ=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789045128; v=1; x=1789649928; b=c949H3Q9PbRB72Uy+dGsmRmUNkOAaYUX8Sc8tbx/AzkaRmCLQc+oDkIRVqn79FjgGfUtKsHk yecC27LjK9cmkO81mYQz1/CHuvfBaYK33JsAFh8yekESXLdBELFhP1zXmMGO+ow4CnFRz+IJX7M ePvdgBtn068YrWEYRIuX6Rto= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id d248a60d230e97a6; Thu, 10 Sep 2026 12:58:48 +0000 X-Mizu-Trace-ID: d248a60d230e97a6 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: tj@kernel.org, josef@toxicopanda.com, axboe@kernel.dk Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, andrii@kernel.org, ast@kernel.org, daniel@iogearbox.net, linux-kselftest@vger.kernel.org, cui.tao@linux.dev, cuitao@kylinos.cn Subject: [RFC PATCH v2 4/5] selftests/bpf: add multi-stream sequentiality example model Date: Thu, 10 Sep 2026 20:58:16 +0800 Message-ID: <20260910125817.223354-5-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260910125817.223354-1-cui.tao@linux.dev> References: <20260910125817.223354-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui Add a second example cost model which replaces the builtin single-cursor sequentiality heuristic with a per-cgroup table of stream slots: an IO is sequential iff its sector matches the expected next sector of any tracked stream. Interleaved sequential readers in one cgroup keep their own slots instead of ping-ponging a single cursor, and random IO inside a hot window rarely matches a moving expectation. Merged bios skip the base cost but still advance the matched stream position, so a merge at the expected sector does not make the following new IO look random. Stream state lives in a CGRP_STORAGE map keyed by the cgroup of the blkcg argument, following the cgroup lifetime; there is no fixed-size registry to exhaust. Measured (QEMU, virtio-blk with the HDD profile, 4k IOs, w=1000): two sequential readers in one cgroup are priced 1961us/op by the builtin model (judged random) and 23us/op by this model (judged sequential), the completed IO count rises from 4495 to 207505; random IO inside an 8M window is priced 24us/op by builtin (undercharge) and 2607us/op by this model; single-stream sequential and whole-disk random pricing are unchanged. --- tools/testing/selftests/bpf/progs/iocost_ms.c | 136 ++++++++++++++++++ 1 file changed, 136 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/iocost_ms.c diff --git a/tools/testing/selftests/bpf/progs/iocost_ms.c b/tools/testing/selftests/bpf/progs/iocost_ms.c new file mode 100644 index 000000000000..3cc57c03d3c8 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/iocost_ms.c @@ -0,0 +1,136 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Example multi-stream sequentiality detection cost model. + * + * The builtin model keeps a single cursor per cgroup, so two + * interleaved sequential readers in one cgroup are all priced random + * (measured 89x overcharge, 12.9x throughput collapse), while random + * IO inside a hot window smaller than the 16MB seek threshold is + * priced sequential (measured 107x undercharge). This model replaces + * the single cursor with a per-cgroup table of stream slots: an IO is + * sequential iff its sector matches the expected next sector of any + * tracked stream. Interleaved streams keep their own slots, and + * windowed random IO rarely matches a moving expectation. + * + * Stream state lives in a CGRP_STORAGE map, so it is created and + * freed with the cgroup. The model implements the full builtin + * linear formula itself, including flush pricing. + */ +#include "vmlinux.h" +#include +#include + +/* VTIME_PER_SEC comes from vmlinux.h (a BTF enum constant) */ +#define IOC_PAGE_SIZE 4096 +#define IOC_SECT_TO_PAGE_SHIFT 3 /* 512B sectors to 4kB pages */ +#define LCOEF_RANDIO_PAGES 4096 /* 16MB seek threshold */ +#define IOCOST_COST_F_MERGE (1ULL << 0) /* not in BTF: a plain macro */ +#define IOCOST_REQ_OP_MASK 0xff /* REQ_OP_MASK, not in BTF */ + +/* + * DIV64_U64_ROUND_UP / DIV_ROUND_UP_ULL equivalents, folded at + * compile time + */ +#define RU(x, y) ((x) / (y) + (((x) % (y)) ? 1 : 0)) + +#define RBPS 174019176ULL +#define RSEQIOPS 41708ULL +#define RRANDIOPS 370ULL +#define WBPS 178075866ULL +#define WSEQIOPS 42705ULL +#define WRANDIOPS 378ULL + +#define RPAGE (RU(VTIME_PER_SEC, RU(RBPS, IOC_PAGE_SIZE))) +#define RSEQIO (RU(VTIME_PER_SEC, RSEQIOPS) - RPAGE) +#define RRANDIO (RU(VTIME_PER_SEC, RRANDIOPS) - RPAGE) +#define WPAGE (RU(VTIME_PER_SEC, RU(WBPS, IOC_PAGE_SIZE))) +#define WSEQIO (RU(VTIME_PER_SEC, WSEQIOPS) - WPAGE) +#define WRANDIO (RU(VTIME_PER_SEC, WRANDIOPS) - WPAGE) + +#define NSLOTS 4 + +struct streams { + __u64 expected[NSLOTS]; /* next expected sector, per stream */ + __u64 stamp[NSLOTS]; /* LRU stamp, 0 = empty */ +}; + +/* + * per-cgroup stream table: keyed by the cgroup, freed with it + */ +struct { + __uint(type, BPF_MAP_TYPE_CGRP_STORAGE); + __uint(map_flags, BPF_F_NO_PREALLOC); + __type(key, int); + __type(value, struct streams); +} stream_tab SEC(".maps"); + +SEC("struct_ops") +u64 BPF_PROG(iocost_ms_calc_cost, u64 opf, u64 nbytes, u64 sector, + struct blkcg *blkcg, u64 model_flags) +{ + struct streams *s; + u64 pages, base, coef_page, randio, advance, now; + u32 i, victim = 0, found = 0xFFFFFFFF; + + if ((opf & IOCOST_REQ_OP_MASK) == REQ_OP_READ) { + base = RSEQIO; coef_page = RPAGE; randio = RRANDIO; + } else if ((opf & IOCOST_REQ_OP_MASK) == REQ_OP_WRITE) { + base = WSEQIO; coef_page = WPAGE; randio = WRANDIO; + } else { + /* + * a fully owning model must price every op; unknown + * ops are priced as a single page write + */ + base = 0; coef_page = WPAGE; randio = 0; + } + advance = RU(nbytes, 512); /* sectors */ + + s = bpf_cgrp_storage_get(&stream_tab, blkcg->css.cgroup, NULL, + BPF_LOCAL_STORAGE_GET_F_CREATE); + if (!s) + return base + RU(nbytes, IOC_PAGE_SIZE) * coef_page; + + now = bpf_ktime_get_ns(); + for (i = 0; i < NSLOTS; i++) { + if (s->expected[i] == sector && s->stamp[i]) { + found = i; + break; + } + } + if (found != 0xFFFFFFFF) { + /* sequential: keep the seq base from the op branch */ + s->expected[found] = sector + advance; + s->stamp[found] = now; + } else { + base = randio; + for (i = 1; i < NSLOTS; i++) { + if (s->stamp[i] < s->stamp[victim]) + victim = i; + } + s->expected[victim] = sector + advance; + s->stamp[victim] = now; + } + + pages = RU(nbytes, IOC_PAGE_SIZE); + if (!pages) + pages = 1; /* dataless flush: one page */ + if (model_flags & IOCOST_COST_F_MERGE) { + /* + * merged bios skip the base cost but still advance + * the stream position above, so a merge at the + * expected sector does not make the following new IO + * look random + */ + base = 0; + } + + return base + pages * coef_page; +} + +SEC(".struct_ops") +struct iocost_model_ops iocost_ms = { + .calc_cost = (void *)iocost_ms_calc_cost, + .name = "iocost_ms", +}; + +char LICENSE[] SEC("license") = "GPL"; -- 2.43.0