From: Tejun Heo <tj@kernel.org>
To: Tao Cui <cui.tao@linux.dev>
Cc: tj@kernel.org, josef@toxicopanda.com, axboe@kernel.dk,
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, Tao Cui <cuitao@kylinos.cn>
Subject: Re: [RFC PATCH 7/8] selftests/bpf: add multi-stream sequentiality example model
Date: Tue, 08 Sep 2026 10:31:11 -1000 [thread overview]
Message-ID: <178889947168.2.15328144500557108713@kernel.org> (raw)
In-Reply-To: <20260908100143.47598-8-cui.tao@linux.dev>
Hello, Tao.
On Tue, 08 Sep 2026 18:01:42 +0800, Tao Cui wrote:
> + if (flags & IOCOST_COST_F_MERGE) {
> + base = 0;
> + goto out;
Please advance the stream position for merged bios too. With 4K IOs, a new
request at sector S sets expected to S+8. A merged bio at S+8 leaves it
there, so the next new request at S+16 is priced random.
> + s = bpf_map_lookup_elem(&stream_tab, &iocg_id);
> + if (!s)
> + return seqio + RU(nbytes, IOC_PAGE_SIZE) * page;
Once the 64-entry map fills, every new cgroup receives sequential prices,
including for random IO. Please note this limitation in the example.
Thanks.
--
tejun
next prev parent reply other threads:[~2026-09-08 21:03 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-08 10:01 [RFC PATCH 0/8] blk-iocost: BPF struct_ops cost model Tao Cui
2026-09-08 10:01 ` [RFC PATCH 1/8] blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary Tao Cui
2026-09-08 10:01 ` [RFC PATCH 2/8] blk-iocost: define iocost_model_ops cost model interface Tao Cui
2026-09-08 10:13 ` sashiko-bot
2026-09-08 20:31 ` Tejun Heo
2026-09-08 10:01 ` [RFC PATCH 3/8] blk-iocost: implement BPF struct_ops registration Tao Cui
2026-09-08 20:31 ` Tejun Heo
2026-09-08 10:01 ` [RFC PATCH 4/8] blk-iocost: dispatch cost calculation to registered BPF model Tao Cui
2026-09-08 20:31 ` Tejun Heo
2026-09-08 10:01 ` [RFC PATCH 5/8] blk-iocost: add ctrl=bpf per-device opt-in Tao Cui
2026-09-08 10:01 ` [RFC PATCH 6/8] selftests/bpf: add iocost cost model test Tao Cui
2026-09-08 10:20 ` sashiko-bot
2026-09-08 20:31 ` Tejun Heo
2026-09-08 10:01 ` [RFC PATCH 7/8] selftests/bpf: add multi-stream sequentiality example model Tao Cui
2026-09-08 10:21 ` sashiko-bot
2026-09-08 20:31 ` Tejun Heo [this message]
2026-09-08 10:01 ` [RFC PATCH 8/8] docs: cgroup-v2: document io.cost ctrl=bpf option Tao Cui
2026-09-08 20:31 ` [RFC PATCH 0/8] blk-iocost: BPF struct_ops cost model Tejun Heo
2026-09-09 13:12 ` Tao Cui
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