Messages in this thread | | | From | Alex Tomas <> | Subject | Re: [RFC] ext4-block-reservation.patch | Date | Sun, 24 Dec 2006 01:47:00 +0300 |
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Hi,
>>>>> Andrew Morton (AM) writes:
AM> Should be ____cacheline_aligned_in_smp.
AM> That's assuming it needs to be cacheline aligned at all. It can consume a AM> lot of space.
the idea is to make block reservation cheap because it's called for every page.
AM> <looks>
AM> oh, this should be allocated with alloc_percpu(), in which case the AM> open-coded alignment can perhaps go away.
got it.
>> + >> +int ext4_reserve_local(struct super_block *sb, int blocks) >> +{ >> + struct ext4_sb_info *sbi = EXT4_SB(sb); >> + struct ext4_reservation_slot *rs; >> + int rc = -ENOSPC; >> + >> + preempt_disable(); >> + rs = sbi->s_reservation_slots + smp_processor_id();
AM> use get_cpu() here.
ok.
>> +void ext4_rebalance_reservation(struct ext4_reservation_slot *rs, __u64 free) >> +{ >> + int i, used_slots = 0; >> + __u64 chunk; >> + >> + /* let's know what slots have been used */ >> + for (i = 0; i < NR_CPUS; i++) >> + if (rs[i].rs_reserved || i == smp_processor_id()) >> + used_slots++; >> + >> + /* chunk is a number of block every used >> + * slot will get. make sure it isn't 0 */ >> + chunk = free + used_slots - 1; >> + do_div(chunk, used_slots); >> + >> + for (i = 0; i < NR_CPUS; i++) {
AM> all these NR_CPUS loops need to go away. Use either AM> for_each_possible_cpu() or, preferably, for_each_online_cpu() and a hotplug AM> notifier.
hmm, i see.
AM> Why is this code using per-cpu data at all, btw? These optimisations tend AM> to be marginal in filesystems. What is the perfomance impact of making AM> this data be single-superblock-wide-instance?
well, even on 2way box a single-lock reservation was in top10.
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