Re: [PATCH v5 10/10] module: Rework module_addr_{min,max}

From: Rusty Russell
Date: Mon Apr 13 2015 - 22:58:07 EST

Ingo Molnar <mingo@xxxxxxxxxx> writes:
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> __module_address() does an initial bound check before doing the
>> {list/tree} iteration to find the actual module. The bound variables
>> are nowhere near the mod_tree cacheline, in fact they're nowhere
>> near one another.
>> module_addr_min lives in .data while module_addr_max lives in .bss
>> (smarty pants GCC thinks the explicit 0 assignment is a mistake).
>> Rectify this by moving the two variables into a structure together
>> with the latch_tree_root to guarantee they all share the same
>> cacheline and avoid hitting two extra cachelines for the lookup.
>> While reworking the bounds code, move the bound update from
>> allocation to insertion time, this avoids updating the bounds for a
>> few error paths.
>> +static struct mod_tree_root {
>> + struct latch_tree_root root;
>> + unsigned long addr_min;
>> + unsigned long addr_max;
>> +} mod_tree __cacheline_aligned = {
>> + .addr_min = -1UL,
>> +};
>> +
>> +#define module_addr_min mod_tree.addr_min
>> +#define module_addr_max mod_tree.addr_max

Nice catch.

Does the min/max comparison still win us anything? (I'm guessing yes...)

In general, I'm happy with this series. Assume you want another
go-round for Ingo's tweaks, then I'll take them for 4.2.

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