  We consider the following shared-resource scheduling problem: Given a set of
jobs $J$, for each $j\in J$ we must schedule a job-specific processing volume
of $v_j>0$. A total resource of $1$ is available at any time. Jobs have a
resource requirement $r_j\in[0,1]$, and the resources assigned to them may vary
over time. However, assigning them less will cause a proportional slowdown.
  We consider two settings. In the first, we seek to minimize the makespan in
an online setting: The resource assignment of a job must be fixed before the
next job arrives. Here we give an optimal $e/(e-1)$-competitive algorithm with
runtime $\mathcal{O}(n\cdot \log n)$. In the second, we aim to minimize the
total completion time. We use a continuous linear programming (CLP) formulation
for the fractional total completion time and combine it with a previously known
dominance property from malleable job scheduling to obtain a lower bound on the
total completion time. We extract structural properties by considering a
geometrical representation of a CLP's primal-dual pair. We combine the CLP
schedule with a greedy schedule to obtain a $(3/2+\varepsilon)$-approximation
for this setting. This improves upon the so far best-known approximation factor
of $2$.
