[lustre-discuss] Degraded read performance with Large Bulk IO (16MB RPC)
Moreno Diego (ID SIS)
diego.moreno at id.ethz.ch
Tue Dec 10 02:05:09 PST 2019
With that kind of degradation performance on read I would immediately think on llite’s max_read_ahead parameters on the client. Specifically these 2:
max_read_ahead_mb: total amount of MB allocated for read ahead, usually quite low for bandwidth benchmarking purposes and when there’re several files per client
max_read_ahead_per_file_mb: the default is quite low for 16MB RPCs (only a few RPCs per file)
You probably need to check the effect increasing both of them.
From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Pinkesh Valdria <pinkesh.valdria at oracle.com>
Date: Tuesday, 10 December 2019 at 09:40
To: "lustre-discuss at lists.lustre.org" <lustre-discuss at lists.lustre.org>
Subject: [lustre-discuss] Degraded read performance with Large Bulk IO (16MB RPC)
I was expecting better or same read performance with Large Bulk IO (16MB RPC), but I see degradation in performance. Do I need to tune any other parameter to benefit from Large Bulk IO? Appreciate if I can get any pointers to troubleshoot further.
- Read: 2563 MB/s
- Write: 2585 MB/s
- Read: 1527 MB/s. (down by ~1025)
- Write: 2859 MB/s
Changes I did are:
- lctl set_param obdfilter.lfsbv-*.brw_size=16
- unmounted and remounted
- lctl set_param osc.lfsbv-OST*.max_pages_per_rpc=4096 (got auto-updated after re-mount)
- lctl set_param osc.*.max_rpcs_in_flight=64 (Had to manually increase this to 64, since after re-mount, it was auto-set to 8, but read/write performance was poor)
- lctl set_param osc.*.max_dirty_mb=2040. (setting the value to 2048 was failing with : Numerical result out of range error. Previously it was set to 2000 when I got good performance.
My other settings:
- lnetctl net add --net tcp1 --if $interface –peer-timeout 180 –peer-credits 128 –credits 1024
- echo "options ksocklnd nscheds=10 sock_timeout=100 credits=2560 peer_credits=63 enable_irq_affinity=0" > /etc/modprobe.d/ksocklnd.conf
- lfs setstripe -c 1 -S 1M /mnt/mdt_bv/test1
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