netdev - Re: [PATCH] qed: allow sleep in qed_mcp_trace

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Date:   Tue, 20 Dec 2022 10:55:00 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Caleb Sander <csander@...estorage.com>,
        Ariel Elior <aelior@...vell.com>,
        Manish Chopra <manishc@...vell.com>, netdev@...r.kernel.org
Cc:     Joern Engel <joern@...estorage.com>
Subject: Re: [PATCH] qed: allow sleep in qed_mcp_trace_dump()

On Sat, 2022-12-17 at 10:56 -0700, Caleb Sander wrote:
> By default, qed_mcp_cmd_and_union() waits for 10us at a time
> in a loop that can run 500K times, so calls to qed_mcp_nvm_rd_cmd()
> may block the current thread for over 5s.
> We observed thread scheduling delays of over 700ms in production,
> with stacktraces pointing to this code as the culprit.

IMHO this is material eligible for the net tree...

> 
> qed_mcp_trace_dump() is called from ethtool, so sleeping is permitted.
> It already can sleep in qed_mcp_halt(), which calls qed_mcp_cmd().
> Add a "can sleep" parameter to qed_find_nvram_image() and
> qed_nvram_read() so they can sleep during qed_mcp_trace_dump().
> qed_mcp_trace_get_meta_info() and qed_mcp_trace_read_meta(),
> called only by qed_mcp_trace_dump(), allow these functions to sleep.
> It's not clear to me that the other caller (qed_grc_dump_mcp_hw_dump())
> can sleep, so it keeps b_can_sleep set to false.

...but we need a suitable Fixes tag here. Please repost specifying the
target tree into the subject and adding the relevant tag, thanks!

Paolo