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Re: [PATCH RFC] xen: Annotate printk() as cold
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Feb 2023 12:08:28 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Feb 2023 11:08:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.02.2023 14:13, Andrew Cooper wrote:
> There is no such thing as a fastpath with a printk() on it, making printk() an
> excellent heuristic for slowpaths.
>
> Net delta is:
>
> add/remove: 595/2 grow/shrink: 56/762 up/down: 70879/-87331 (-16452)
> Total: Before=4085425, After=4068973, chg -0.40%
>
> because cold functions are optimised differently. For example, one function
> with a particularly large swing is:
>
> vmcs_dump_vcpu.cold - 2172 +2172
> vmcs_dump_vcpu 7030 408 -6622
>
> with a net delta of 7030 down to 4450.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> There are other functions which will be good heuristics to annotate, but we
> probaby want to collect .cold together in one location rather than having them
> spread out across all translation units.
Doesn't the compiler put it in .text.cold? Or is that compiler variant
and/or version dependent?
Jan
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