nqnfs.me

早期freebsd实现

"Leases" at 3.725,8.547 rjust
"Leases, Rdirlookup" at 3.725,8.397 rjust
"Leases, Attrib leases, Rdirlookup" at 3.725,8.247 rjust
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"10" at 0.825,8.410 rjust
"15" at 0.825,8.697 rjust
"20" at 0.825,8.997 rjust
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"10" at 4.438,7.660
"Time (sec)" at 0.150,8.997
"Number of Clients" at 2.837,7.510
"Figure #4: MAB Phase 4 (grep/wc/find)" at 2.837,10.335
"NFS" at 3.725,8.697 rjust
"Leases" at 3.725,8.547 rjust
"Leases, Rdirlookup" at 3.725,8.397 rjust
"Leases, Attrib leases, Rdirlookup" at 3.725,8.247 rjust
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"Time (sec)" at 0.150,8.997
"Number of Clients" at 2.837,7.510
"Figure #5: MAB Phase 5 (compile)" at 2.837,10.335
"NFS" at 3.725,8.597 rjust
"Leases" at 3.725,8.447 rjust
"Leases, Rdirlookup" at 3.725,8.297 rjust
"Leases, Attrib leases, Rdirlookup" at 3.725,8.147 rjust
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.pp
In figure 2, where a subtree of seventy small files is copied, the difference between the protocol variants is minimal,
with the NQNFS variants performing slightly better.
For this case, the Readdir_and_Lookup RPC is a slight hindrance under heavy
load, possibly because it results in larger directory blocks in the buffer
cache.
.pp
In figure 3, for the phase that gets file attributes for a large number
of files, the leasing variants take about 50% longer, indicating that
there are performance problems in this area. For the case where valid
current leases are required for every file when attributes are returned,
the performance is significantly worse than when the attributes are allowed
to be stale by a few seconds on the client.
I have not been able to explain the oscillation in the curves for the
Lease cases.
.pp
For the string searching phase depicted in figure 4, the leasing variants
that do not require valid leases for files when attributes are returned
appear to scale better with server load than NFS.
However, the effect appears to be
negligible until the server load is fairly heavy.
.pp
Most of the time in the MAB benchmark is spent in the compilation phase
and this is where the differences between caching methods are most
pronounced.
In figure 5 it can be seen that any protocol variant using Leases performs
about a factor of two better than NFS
at a load of ten clients. This indicates that the use of NQNFS may
allow servers to handle significantly more clients for this type of
workload.
.pp
Table 2 summarizes the MAB run times for all phases for the single client
DECstation 5000/25. The \fILeases\fR case refers to using leases, whereas
the \fILeases, Rdirl\fR case uses the Readdir_and_Lookup RPC as well and
the \fIBCache Only\fR case uses leases, but only the buffer cache and not
the attribute or name caches.
The \fINo Caching\fR cases does not do any client side caching, performing
all system calls via synchronous RPCs to the server.
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Table #2: Single DECstation 5000/25 Client Elapsed Times (sec)
Phase	1	2	3	4	5	Total	% Improvement
_
No Caching	6	35	41	40	258	380	-93
NFS	5	24	15	20	133	197	0
BCache Only	5	20	24	23	116	188	5
Leases, Rdirl	5	20	21	20	105	171	13
Leases	5	19	21	21	99	165	16
.TE
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.sh 2 "Processor Speed Tests"
.pp
An important goal of client-side file system caching is to decouple the
I/O system calls from the underlying distributed file system, so that the
client's system performance might scale with processor speed. In order
to test this, a series of MAB runs were performed on three
DECstations that are similar except for processor speed.
In addition to the four protocol variants used for the above tests, runs
were done with the client caches turned off, for
worst case performance numbers for caching mechanisms with a 100% miss rate. The CPU utilization
was measured, as an indicator of how much the processor was blocking for
I/O system calls. Note that since the systems were running in single user mode
and otherwise quiescent, almost all CPU activity was directly related
to the MAB run.
The results are presented in
table 3.
The CPU time is simply the product of the CPU utilization and
elapsed running time and, as such, is the optimistic bound on performance
achievable with an ideal client caching scheme that never blocks for I/O.
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Table #3: MAB Phase 5 (compile)
	DS2100 (10.5 MIPS)	DS3100 (14.0 MIPS)	DS5000/25 (26.7 MIPS)
	Elapsed	CPU	CPU	Elapsed	CPU	CPU	Elapsed	CPU	CPU
	time	Util(%)	time	time	Util(%)	time	time	Util(%)	time
_
Leases	143	89	127	113	87	98	99	89	88
Leases, Rdirl	150	89	134	110	91	100	105	88	92
BCache Only	169	85	144	129	78	101	116	75	87
NFS	172	77	132	135	74	100	133	71	94
No Caching	330	47	155	256	41	105	258	39	101
.TE
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As can be seen in the table, any caching mechanism achieves significantly
better performance than when caching is disabled, roughly doubling the CPU
utilization with a corresponding reduction in run time. For NFS, the CPU
utilization is dropping with increase in CPU speed, which would suggest that
it is not scaling with CPU speed. For the NQNFS variants, the CPU utilization
remains at just below 90%, which suggests that the caching mechanism is working
well and scaling within this CPU range.
Note that for this benchmark, the ratio of CPU times for
the DECstation 3100 and DECstation 5000/25 are quite different than the
Dhrystone MIPS ratings would suggest.
.pp
Overall, the results seem encouraging, although it remains t