Commits on Jun 28, 2019

1. Reduce sunrpc.tcp_max_slot_table_entries …

   PR #93 did not work as expected.
   
   Further analysis showed, that the parallelism of page io
   (which includes buffered reads) is not limit by nfs.max_session_slots
   but by sunrpc.tcp_max_slot_table_entries.
   
   The default value is 65536 ( RPC_MAX_SLOT_TABLE_LIMIT ).
   
   This parameter can be modified for the running system via
   /proc/sys/sunrpc/tcp_max_slot_table_entries and is applied to
   new server connections.
   
   Experiment (on simsalabimbambasaladusaladim) :
   
       # preload server cache
       ssh mrtorgue cat /project/stresser/files/random_10G.dat \> /dev/null
   
       umount /project/stresser
       echo 3 > /proc/sys/vm/drop_caches
       time cat /project/stresser/files/random_10G.dat > /dev/null
   
       # result: 0m11.429s  ca. 14 nfsd visible active in `top` on server
   
       echo 4 > /proc/sys/sunrpc/tcp_max_slot_table_entries
       umount /project/stresser
       echo 3 > /proc/sys/vm/drop_caches
       time cat /project/stresser/files/random_10G.dat > /dev/null
   
       # 0m12.546s , 4 nfsd visible active in `top` on server
   
       echo 65536 > /proc/sys/sunrpc/tcp_max_slot_table_entries
       umount /project/stresser
       echo 3 > /proc/sys/vm/drop_caches
       time cat /project/stresser/files/random_10G.dat > /dev/null
   
       # result: 0m11.937s , ca. 16 nfsd visible active in `top` on server
   
   Reduce sunrpc.tcp_max_slot_table_entries to 4 instead of nfs.max_session_slots

   

   donald committed Jun 28, 2019
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