[lustre-discuss] Degraded read performance with Large Bulk IO (16MB RPC)

[Moreno Diego (ID SIS)]

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.

Regards,

Diego


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.

Throughput before

-          Read:  2563 MB/s

-          Write:  2585 MB/s

Throughput after

-          Read:  1527 MB/s. (down by ~1025)

-          Write:  2859 MB/s


Changes I did are:
On oss

-          lctl set_param obdfilter.lfsbv-*.brw_size=16

On clients

-          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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